Connexin 30 (GJB6) deletion as a cause of a false positive sweat test result

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There are several reports in the literature regarding conditions that are known to be associated with a false positive result. In aim of this article is describing a previously unreported cause of a false positive sweat test (ST). Methods : An observational, cross-sectional single-center study was performed. We recruited three patients with a neurosensory deafness caused by a deletion in both alleles of connexin 30. The first-degree relatives of these three patients with hearing impairment due to other mutations were also included. A ST was performed in all the selected cases. Results : Among the three patients with a deletion in both connexin 30 alleles, two had a positive ST, whereas the third patient had a close-to-positivity borderline result (57 mmol/L). Moreover, there were no positive sweat tests in individuals with other mutation patterns. Conclusion : Patients with affection of both alleles of connexin 30 were the only ones to show a positive ST, which may translate a higher risk of hyponatremic dehydration. The reason of the ST positivity remains unclear and may be related to the fact that connexin 30 plays a role modulating other molecules in both inner ear and sweat glands. sweat test connexin 30 GJB6 and neurosensory deafness What is Known The sweat test is the gold standard for the diagnosis of cystic fibrosis. However, the causes of false positives in the test are increasingly recognized. What is New: This study describes a previously unreported cause of a false positive sweat test. Three patients with homozygous mutations in the connexin 30 gene are described. All of them had an abnormal sweat test, and two of them presented with severe hyponatremic dehydration. INTRODUCTION The sweat test (ST) consists of a measurement of sweat chloride concentration and conductivity in a sample of sweat. The test is mainly used as the gold standard for the diagnosis of cystic fibrosis (CF). CF is the most common life-threatening autosomal recessive disease in the Caucasian population, due to a multisystem disorder caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR), which encodes a chloride channel[ 1 ]. When a patient presents a positive newborn screen, clinical symptomatology suggesting CF, or a positive family history, a diagnosis of CF can be made if the ST is pathological. An ST showing a chloride concentration greater than 60 mmol/L is considered as pathological; values between 30 and 60 mmol/L, as borderline results; whereas values less than 30 mmol/L are considered as normal ones [ 2 ]. However, there are several reports in the literature regarding conditions that are known to be associated with false positive or false negative ST results. The list of these conditions has grown significantly over time. Some examples include malnutrition, some metabolic disorders (such as mucopolysaccharidosis, type I fucosidosis or glycogen storage diseases), dermatological diseases (as congenital ectodermal dysplasia or atopic dermatitis), various endocrine disorders (e.g: panhypopituitarism, Addison disease, isolated adrenocorticoid deficiency, vasopressin-resistant diabetes insipidus, hypothyroidism and hypoparathyroidism) and carbonic anhydrase XII mutations [ 3 ],[ 4 ]. In this article, we describe a previously unreported cause of false-positive ST: we identified three patients with a mutation in both alleles of the Gap Junction Beta ( GJB ) 6 gene (encoding connexin 30, which is responsible for hearing impairment) in which no other potential causes of a positive result were found. Hearing impairment is a disabling disease with the highest rate of age-standardized disability worldwide. Globally, the prevalence of congenital hearing impairment is 1–3 in 1000 children at birth or during early childhood [ 5 ]. Nonsyndromic hearing impairment (NSHI) is the most common form of neurosensory deafness, accounting for almost 70% of inherited hearing impairments. The majority of NHSI cases have an autosomal recessive pattern of inheritance [ 6 ]. The connexin gene family is the most prevalent gene that contributes to NSHI. Studies in European and Asian populations have identified pathogenic variants in GJB2 (encoding connexin 26) and GJB6 (encoding connexin 30) as the major contributors to autosomal recessive NSHI (ARNSHI). GJB2-c35delG is the most prevalent variant (20–50%) found in cases of ARNSHI. The GJB6-D13S1830 deletion was identified in up to 9.7% of cases and thus is the second-largest contributor to the genetic etiology of NSHI in European populations, either with homozygous presentation or when present in addition to a GJB2 mutation on the opposite allele [ 6 ]–[ 10 ]. Connexins are a multigene family of at least 20 distinct integral membrane proteins in humans that are expressed throughout the body in overlapping and unique patterns. Six connexins can form a connexon, a specialized intracellular structure surrounding a pore. Two connexons in opposing cell membranes can align to form an intercellular gap junction. Gap junctions are aqueous intercellular channels that are found in all tissues of the human body, including skin, nervous tissue, cochlea, heart, and muscle [ 11 ]. By connecting neighboring cells together, gap junctions allow direct cell-to-cell communication via the rapid transfer of physiological signals, ions, water, and small nutrients, which is pivotal for the coordination and synchronization of cellular responses to internal and external stimuli. In recent years, mutations in the skin-expressed connexin genes GJB2 (connexin 26), GJB3, GJB4 (connexin 31 and 30.3), GJB6 (connexin 30), and Gap Junction Alpha 1 (connexin 43) have been linked to human hereditary diseases affecting both the epidermis and cochlea [ 11 ]. MATERIAL AND METHODS This was an observational, cross-sectional single-center study. The first case was a 22-month-old female child with neurosensory deafness due to a mutation in homozygosity of both GJB6 alleles. She required multiple admissions due to hyponatremic dehydration. In this context, a ST was performed as part of the study of recurrent hyponatremia, which was positive. CF was ruled out since she did not present other symptoms compatible with CF, her neonatal screening was negative and she had a genetic test with no mutations in CFTR. Four months later, a 13-month-old female child with neurosensory deafness due to a mutation in the compound heterozygosity of both GJB6 alleles was also admitted due to a hyponatremic dehydration. Considering the previous case, a ST was also performed, resulting in a chloride concentration of 57 mmol/L. Similarly, no other symptoms of CF were observed and no mutations were detected in the CFTR gene. Following these findings, the hospital’s genetic database was accessed in order to search for other patients with neurosensory deafness caused by a mutation in homozygosity or compound heterozygosity for connexin 30. Although no other pediatric patients were found, we identified an adult man with deafness with a mutation in the compound heterozygosity of both GJB6 alleles (third case). This patient was examined in 2009 as part of a genetic study of his daughters, who also have deafness. The first-degree relatives of these three patients with hearing impairment due to a mutation in both GJB6 alleles were also included. Informed consent was obtained from each participant. This study was approved by the Hospital Sant Joan de Déu Ethics Committee (Esplugues, Spain, refPIC-115-24) and was done in accordance with the Declaration of Helsinki. Informed consent was obtained from the individual participants included in the study or their parents. A ST was performed in all the selected cases. ST is a noninvasive test that is used for the determination of chloride in sweat. The first part of the test involves iontophoresis. In our center, it is performed with the Webster Sweat Inducer–Wescor® system. Two electrodes (anode and cathode) with one disk each of pilocarpine (Pilogel®) are placed on the cleaned skin of the anterior part of the forearm. After 5 minutes of stimulation, the discs are removed and the skin surface is cleaned again. Immediately, the Macroduct® system collector is fixed. This is made up of a 0.6 mm capillary in diameter arranged in a spiral shape in a concave plastic disc with a central opening to collect sweat, which turns blue as it fills, to making it easier to see the amount collected. The required sample volume is 20–50 µl, which is collected for a minimum period of 20 minutes and a maximum of 30 minutes. After the sample is detected to be sufficient, the collector is removed from the forearm and is immediately manipulated by the CF nurse to determine conductivity via Sweat-Check 3120, Wescor® and chlorodimetry via Chloride Analyzer 926, Sherwood Scientific Ltd. Prior to every intervention, the corresponding quality control was carried out with the Macroduct ® system equipment. In cases 1 and 2, genetic tests were performed in order to rule out mutations in CFTR gene. Initially Elucigene CF-EU2 kit test was done. Then, a direct sequencing of the coding region of the gene was performed. In addition, deletions/duplications of the CFTR gene were analyzed by Multiplex Ligation-dependent Probe Amplification (MLPA) using the SALSA MLPA P091D2 kit (MRC Holland®). The results were obtained in an automatic sequencer ABI3130. This technique detects more than 99% of mutations in the CFTR gene [ 12 ]. On the other hand, deletions in the GJB6 gene were obtained by using the SALSA MLPA P163-GJB-WFS1-POU3F4 kit (MRC Holland®), and analyzed with the Coffalyser program. The Mann-Whitney U test was used to compare medians between groups of patients. The statistical analysis was performed via SPSS v.24, with statistical significance defined as a p-value of < 0.05. RESULTS We recruited three patients with a neurosensory deafness caused by a mutation in both alleles of connexin 30. A ST was also performed in their five relatives with deafness caused by other mutations. The results are described in Table 1 . Among the three patients with a deletion in compound heterozygosis of connexin 30, two had a positive ST, whereas the third patient had a close-to-positivity borderline result (57 mmol/L). Moreover, there were no positive sweat tests in individuals with other mutation patterns. Patients with a deletion in both connexin 30 alleles presented increased chloride concentrations (p-value: 0.036) and conductivity (p-value: 0.035). Table 1 Descriptive features of patients with deafness in which a ST was performed. Patient Index case Age Sex Mutation pattern Sweat test Chloride Conductivity Interpretation Case 1 Yes 22 months Female GJB6 homozygosis: [del(GJB6-D13S1830)] 67 mmol/L 80 mmol/L Abnormal Case 2 Yes 13 months Female GJB6 compound heterozygosis: [del( GJB6 -D13S18 30 ) + del( GJB6 -D13S18 54 )] 57 mmol/L 67 mmol/L Border-line Case 3 Yes 48 years Male GJB6 compound heterozygosis: [del(GJB6-D13S1854) + del(GJB6-D13S1830)] 65 mmol/L 86 mmol/L Abnormal Case 4 Case 1 brother 5 years Male GJB6 / GJB2 in heterozygosis: [del( GJB6 -D13S1830) + GJB2 -c.35delG] 10 mmol/L 44 mmol/L Normal Case 5 Case 1 father 35 years Male GJB6 / GJB2 in heterozygosis: [del( GJB6 -D13S1830) + GJB2 -c.35delG] 23 mmol/L 46 mmol/L Normal Case 6 Case 1 mother 38 years Female GJB6 / GJB2 in heterozygosis: [del( GJB6 -D13S1830) + GJB2 -c.35delG] 12 mmol/L 45 mmol/L Normal Case 7 Case 3 daughter 14 years Female GJB6 heterozygosity: [del(GJB6-D13S1854)] + unknown mutation 20 mmol/L 43 mmol/L Normal Case 8 Case 3 daughter 14 years Female GJB6 heterozygosity: [del(GJB6-D13S1854)] + unknown mutation 25 mmol/L 45 mmol/L Normal Patient 1 is a 22-month-old female child with severe hearing impairment due to a mutation in homozygosis of both GJB6 alleles [del(GJB6-D13S1830)]. She is a bilateral cochlear implant recipient. Both the patient’s parents and her brother (cases 4–6) experienced hearing impairment due to combination of a mutation in the heterozygosity of GJB2 [(GJB2-c.35delG)] and GJB6 [del(GJB6-D13S1830)]. The patient visited the emergency department for vomiting, diarrhea and fever for 48 hours. A blood test revealed metabolic acidosis (pH 7.31, pCO2 30.5 mmHg, bicarbonate concentration 14.9 mmol/L) with a normal ionogram (sodium 136 mmol/L, potassium 4.2 mmol/L, chloride 106 mmol/L) and no increase in acute-phase reactants. Intravenous rehydration was started and the patient was admitted. During hospitalization, a more thorough anamnesis revealed that she had been admitted four times in one year because of hyponatremia (up to 113 mmol/L), metabolic acidosis and dehydration in the context of vomiting and diarrhea. Previously, additional studies revealed no impairments in sodium fractional excretion or in cortisol and renin levels. As part of the study, a ST was performed, which yielded a positive result (with a chloride concentration of 67 mmol/L and conductivity of 80 mmol/L). She was referred to the CF unit, where a new ST test was also positive. Moreover, a genetic test ruled out CF and carbonic anhydrase XII mutations. She never presented with respiratory symptoms or signs of pancreatic insufficiency. As part of the study, a sweat test was also performed on her parents and brother, who were negative (Table 1 ). Patient 2 is a 13-month-old child with severe neurosensory deafness due to a mutation in the compound heterozygosity of GJB6 [del(GJB6-D13S1830) and del(GJB6-D13S1854)] with no family history of deafness. Her father is a carrier in heterozygosity of the mutation del (GJB6-D13S1830) and her mother is a carrier in heterozygosity of the mutation del(GJB6-D13S1854). The patient was admitted directly to the intensive care unit (ICU) due to hypovolemic shock caused by uncontrollable vomiting and refusal to eat for 12 hours in the context of high ambient temperature. Initially, a blood test revealed metabolic acidosis and hyponatremia of 120 mmol/L. During her stay in the ICU, she received inotropic drugs and aggressive rehydration. After the first stabilization in the ICU, she was transferred to the pediatric ward. Owing to a similar case (explained above) that presented with the same mutation, a ST was performed showing close-to-positivity results (chloride of 57 mmol/L and conductivity of 67 mmol/L). Moreover, a genetic test was performed and revealed no mutations related to cystic fibrosis. During 18 months of surveillance, she did not have any respiratory or gastrointestinal symptoms. Patient 3 is a 48 year-old man with neurosensory deafness caused by a mutation in the compound heterozygosity of GJB6 [del(GJB6-D13S1830) and del(GJB6-D13S1854)] who had been studied in 2009 after having had twins with hearing impairment (cases 7–8) due to a GJB6 mutation in heterozygosity. After observing the findings explained above, patient was recruited and a ST was performed, showing a positive result (chloride of 65 mmol/L and conductivity of 86 mmol/L). A thorough anamnesis was performed, and the patient had not experienced episodes of previous dehydration or respiratory or gastrointestinal symptoms. Since the patient was completely asymptomatic, and after observing the relationship between connexin 30 mutation and positive ST, a genetic test to rule out CF was not performed. DISCUSSION As previously mentioned, connexins are expressed not only in the inner ear, but also in other tissues such as sweat glands and the epidermis. These molecules are assembled in order to form gap junctions, which allow the passage of small molecules between adjacent cells in animal tissues, coupling them electrically and metabolically. There are multiple types of connexins (such as 26, 30, 31 and 43). However, they tend to show overlapping expression patterns, and connexones formed by different types of connexins exist [ 13 ]. The ways in which connexins interact with each other and with other molecules are complex. They have paracrine actions, regulating, for instance, calcium and sodium channels [ 13 ]–[ 15 ]. They also have mechanical functions, such as allowing the contraction of the myoepithelial cells of the sweat glands, thus enabling the excretion of sweat [ 16 ]. This wide range of functions depends on subtle factors such as the position of the molecule on the cell surface or how they are placed in relation to other structures on which they exert their effect. Indeed, different types of mutations in connexin alleles affect how and where their molecules are expressed in the cells, as well as how they are transported within them [ 9 ]. This translates into a great variability at the phenotypic level as well. For example, loss-of-function mutations are more related to nonsyndrome deafness, whereas gain-of-function mutations are described in diseases involving both skin and deafness. The G11R mutationin connexin 30, for instance, is related to Clouston syndrome (OMIM #129500), a type of ectodermal dysplasia that affects both hair, nails and skin [ 17 ]. On the other hand, a wide variety of diseases involving connexin 26 have been described. Some of them are nonsyndromic, such as porokeratotic eccrine ostial and dermal duct nevus, in which nevi following a linear Blaschkoid pattern are observed. Many others are syndromic, showing an association between deafness and skin defects, such as keratitis ichthyosis deafness syndrome (OMIM #148210), or palmoplantar keratoderma associated with deafness (OMIM #148350). Although connexins are also expressed in sweat glands, the literature concerning this phenomenon is scarce. In this sense, it is important to highlight a paper describing some patients with connexin 26-related genes [ 18 ]. The authors provided data suggesting that evolutionary balancing of monogenic disorders may be more frequent than presently thought by describing the association between sensory disorders caused by recessive mutations at the connexin 26 and skin alterations. They examined histology and in vitro sweat production among members of families affected by R143W, a GJB2 mutation. They reported that both heterozygous and homozygous participants had a significantly thicker epidermis. Interestingly, only homozygotes presented relatively high concentrations of sodium and chloride in the sweat, which may be interpreted as a biological disadvantage. The reason why mutations in connexins could explain the relatively high concentrations of chloride and sodium in sweat is not clear. It is known that connexin 30 plays a role as a modulator of the activity of epithelial sodium channels (ENaC) via multiple pathways, such as the paracrine secretion of ATP or glutamate or the promotion of clathrin-mediated ENaC endocytosis [ 19 ]. In relation to this fact, Sipos et al. observed that mice with connexin 30 deficiencies had a reduced natriuretic capacity in response to hypertension, as their ability to regulate sodium reabsorption was limited [ 15 ]. These observations emphasize that connexins play a role in regulating sodium transport but would not justify a positivity in the ST. In this regard, the intrinsic actions of connexin 30 are particularly complex and are closely linked to the expression of connexin 26 in both inner ear and sweat glands. Therefore, it has been defined that deletions of the GJB6 gene directly affect the expression of connexin [ 20 ]. More specifically, Common et al. showed a case of a deaf child with a del(GJB6-D13S1830) and GJB2-c.35delG constellation in which a skin biopsy was performed. The authors compared his biopsy results with those of a healthy control and a patient with a heterozygous mutation in the connexin 26 gene. They observed that the case patient, but not the others, showed a marked decrease in the expression of connexin 26 in the duct, but not in the excretory portion of the sweat gland, without affecting the expression of connexin 30 itself; as well as an alteration of keratin expression, which acts supporting many other molecules [ 21 ]. In conclusion, although unabnle to give a definitive explanation, we found that all patients with a mutation affecting both alleles of connexin 30 presented concentrations of chloride in sweat higher than 55 mEq/L. However, those patients with genetic deafness explained by other allelic constellations presented with normal ST. It should be emphasized that these results may be relevant from a clinical point of view. Patients with these mutations could be exposed to a greater risk of dehydration during the first months of life, especially during the hot months in warm countries. In fact, two of the patients in our series required hospital admission, even in the PICU. To the best of our knowledge, this is the first study in which a mutation in connexin 30 has been described as a possible explanation for the positivity of a ST in patients with severe deafness. The most important limitation of our study is the small sample size. This limitation is justified by the low incidence of mutations affecting connexin 30 in our country. In this sense, we think that a multicenter study should be performed to confirm this relationship. Abbreviations ARNSHI: autosomal recessive NSHI. CF: cystic fibrosis. CFTR: cystic fibrosis transmembrane conductance regulator. ENaC: epithelial sodium channels. GJB : Gap junction beta ICU: Intensive Care Unit MLPA: multiplex ligation-dependent probe amplification. NSHI: nonsyndromic hearing impariment. ST: sweat test. Declarations Funding The authors declare that no funds, grants, or other support were received during the preparation of this manuscript. Author Contribution Anna Rossell: ARAleix Soler-García: ASLoreto Martorell: LMAntònia Claveria: ACLaura Valero: LVSílvia Rodríguez: SRCèlia Badenas: CBMaria Cols-Roig: MCAll authors contributed to the study conception and design. Data collection was performed by AR and AS. Material preparation and analysis were performed by AR, AS, LM and MC. Clinical and laboratory tests were performed by SR, LM and CB. A deep critical review was performed by CB, LV and AC. The first draft of the manuscript was written by AR and all authors commented on previous versions of the manuscript. All authors read and approved the fnal manuscript. References Farrell PM, White TB, Ren CL, et al. Diagnosis of Cystic Fibrosis: Consensus Guidelines from the Cystic Fibrosis Foundation. J Pediatr . 2017;181S:S4-S15.e1. Turcios NL. Cystic Fibrosis Lung Disease: An Overview. Respir Care . 2020;65(2):233-251. Feldshtein M, Elkrinawi S, Yerushalmi B, et al. Hyperchlorhidrosis caused by homozygous mutation in CA12, encoding carbonic anhydrase XII. Am J Hum Genet . 2010;87(5):713-720. Guglani L, Stabel D, Weiner DJ. False-Positive and False-Negative Sweat Tests: Systematic Review of the Evidence. Pediatr Allergy Immunol Pulmonol . 2015;28(4):198-211. Mehra S, Eavey RD, Keamy DG. The epidemiology of hearing impairment in the United States: newborns, children, and adolescents. Otolaryngol Head Neck Surg . 2009;140(4):461-472. Snoeckx RL, Huygen PLM, Feldmann D, et al. GJB2 mutations and degree of hearing loss: a multicenter study. Am J Hum Genet . 2005;77(6):945-957. Del Castillo FJ, Rodríguez-Ballesteros M, Álvarez A, et al. A novel deletion involving the connexin-30 gene, del(GJB6-d13s1854), found in trans with mutations in the GJB2 gene (connexin-26) in subjects with DFNB1 non-syndromic hearing impairment. J Med Genet . 2005;42(7):588-594. Wonkam ET, Chimusa E, Noubiap JJ, Adadey SM, Fokouo JVF, Wonkam A. GJB2 and GJB6 Mutations in Hereditary Recessive Non-Syndromic Hearing Impairment in Cameroon. Genes (Basel) . 2019;10(11). Marlin S, Feldmann D, Blons H, et al. GJB2 and GJB6 mutations: genotypic and phenotypic correlations in a large cohort of hearing-impaired patients. Arch Otolaryngol Head Neck Surg . 2005;131(6):481-487. Pandya A, O’Brien A, Kovasala M, Bademci G, Tekin M, Arnos KS. Analyses of del(GJB6-D13S1830) and del(GJB6-D13S1834) deletions in a large cohort with hearing loss: Caveats to interpretation of molecular test results in multiplex families. Mol Genet genomic Med . 2020;8(4). Avshalumova L, Fabrikant J, Koriakos A. Overview of skin diseases linked to connexin gene mutations. Int J Dermatol . 2014;53(2):192-205. Savant A, Lyman B, Bojanowski C, et al. Cystic Fibrosis. Pediatr Pulmonol . 1993;58(11):3013-3022. Lilly E, Sellitto C, Milstone LM, White TW. Connexin channels in congenital skin disorders. Semin Cell Dev Biol . 2016;50:4-12. Richard G. Connexin disorders of the skin. Clin Dermatol . 2005;23(1):23-32. Sipos A, Vargas SL, Toma I, Hanner F, Willecke K, Peti-Peterdi J. Connexin 30 deficiency impairs renal tubular ATP release and pressure natriuresis. J Am Soc Nephrol . 2009;20(8):1724-1732. Nakashima K, Kato H, Kurata R, et al. Gap junction-mediated contraction of myoepithelial cells induces the peristaltic transport of sweat in human eccrine glands. Commun Biol . 2023;6(1). Kutkowska-Kaźmierczak A, Niepokój K, Wertheim-Tysarowska K, et al. Phenotypic variability in gap junction syndromic skin disorders: experience from KID and Clouston syndromes’ clinical diagnostics. J Appl Genet . 2015;56(3):329-337. Meyer CG, Amedofu GK, Brandner JM, Pohland D, Timmann C, Horstmann RD. Selection for deafness? Nat Med . 2002;8(12):1332-1333. Ilyaskin A V., Korbmacher C, Diakov A. Inhibition of the epithelial sodium channel (ENaC) by connexin 30 involves stimulation of clathrin-mediated endocytosis. J Biol Chem . 2021;296. Rodriguez-Paris J, Tamayo ML, Gelvez N, Schrijver I. Allele-specific impairment of GJB2 expression by GJB6 deletion del(GJB6-D13S1854). PLoS One . 2011;6(6). Common JEA, Bitner-Glindzicz M, O’Toole EA, et al. Specific loss of connexin 26 expression in ductal sweat gland epithelium associated with the deletion mutation del(GJB6-D13S1830). Clin Exp Dermatol . 2005;30(6):688-693. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 12 Jun, 2025 Read the published version in European Journal of Pediatrics → Version 1 posted Editorial decision: Revision requested 13 Apr, 2025 Reviews received at journal 13 Apr, 2025 Reviews received at journal 01 Apr, 2025 Reviewers agreed at journal 20 Mar, 2025 Reviewers agreed at journal 19 Mar, 2025 Reviewers agreed at journal 18 Mar, 2025 Reviewers invited by journal 18 Mar, 2025 Editor assigned by journal 17 Mar, 2025 Submission checks completed at journal 17 Mar, 2025 First submitted to journal 12 Mar, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6213266","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":432619768,"identity":"257db60a-3e45-42bb-8fe3-14494a48fc5e","order_by":0,"name":"Anna Rossell","email":"","orcid":"","institution":"Hospital Sant Joan de Déu Barcelona","correspondingAuthor":false,"prefix":"","firstName":"Anna","middleName":"","lastName":"Rossell","suffix":""},{"id":432619772,"identity":"422e0e67-6657-4ff4-8994-63114c9a7aa5","order_by":1,"name":"Aleix Soler-Garcia","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA20lEQVRIie2PsQrCMBRFbwm8Lg+zVpT6CxHBxcFfqYvObrp0EZwU135OSkBHV8FFEJwVl7qZQkEnUzfBnOXlQQ73PsDj+UVCQJezAQQnsKihiEoh+1S1FVQKRa/1A3IhcsNIYwrXl3nRHkBK/VmJDCV5BtMj3vWPzBM0s8QRY1jpK/RoGY3pCDZQB4fRMfKqE6SjZedC08Iqw72jmLKH2BRhU4jAZQocxbqGVJ6p8paxaNlbODo4lHi3ON95lsYy3Aa3x2oQy42jWFWvmsEKXOf/O8W3gsfj8fwDT5dmOFrfScmbAAAAAElFTkSuQmCC","orcid":"","institution":"University of Barcelona","correspondingAuthor":true,"prefix":"","firstName":"Aleix","middleName":"","lastName":"Soler-Garcia","suffix":""},{"id":432619777,"identity":"ce73bda6-6572-45f7-aa36-85484e6eb17e","order_by":2,"name":"Loreto Martorell","email":"","orcid":"","institution":"Hospital Sant Joan de Déu Barcelona","correspondingAuthor":false,"prefix":"","firstName":"Loreto","middleName":"","lastName":"Martorell","suffix":""},{"id":432619779,"identity":"9c5513ff-60cb-4106-a044-837f34fe4e10","order_by":3,"name":"Maria Antonia Claveria","email":"","orcid":"","institution":"Hospital Sant Joan de Déu Barcelona","correspondingAuthor":false,"prefix":"","firstName":"Maria","middleName":"Antonia","lastName":"Claveria","suffix":""},{"id":432619780,"identity":"e121aeb5-fd1c-4dd3-a8b3-828164d94131","order_by":4,"name":"Laura Valero","email":"","orcid":"","institution":"Hospital Sant Joan de Déu Barcelona","correspondingAuthor":false,"prefix":"","firstName":"Laura","middleName":"","lastName":"Valero","suffix":""},{"id":432619781,"identity":"30d46ba9-f0e5-4b64-b4e1-de3a97aa6aff","order_by":5,"name":"Sílvia Rodríguez","email":"","orcid":"","institution":"Hospital Sant Joan de Déu Barcelona","correspondingAuthor":false,"prefix":"","firstName":"Sílvia","middleName":"","lastName":"Rodríguez","suffix":""},{"id":432619782,"identity":"cf0418ec-bd95-490e-8793-4354a89d0133","order_by":6,"name":"Cèlia Badenas","email":"","orcid":"","institution":"Hospital Clínic de Barcelona","correspondingAuthor":false,"prefix":"","firstName":"Cèlia","middleName":"","lastName":"Badenas","suffix":""},{"id":432619783,"identity":"377fd92a-53cc-4527-9c87-69d8de9d8440","order_by":7,"name":"Maria Cols-Roig","email":"","orcid":"","institution":"Hospital Sant Joan de Déu Barcelona","correspondingAuthor":false,"prefix":"","firstName":"Maria","middleName":"","lastName":"Cols-Roig","suffix":""}],"badges":[],"createdAt":"2025-03-12 15:08:23","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6213266/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6213266/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00431-025-06220-7","type":"published","date":"2025-06-12T15:57:03+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":84726460,"identity":"778bceb3-6d68-46ae-9a0e-8c870943f97c","added_by":"auto","created_at":"2025-06-16 16:04:29","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":539761,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6213266/v1/6c270e39-6c7e-40bb-8987-a97c6b05feab.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Connexin 30 (GJB6) deletion as a cause of a false positive sweat test result","fulltext":[{"header":"What is Known","content":"\u003cp\u003eThe sweat test is the gold standard for the diagnosis of cystic fibrosis. However, the causes of false positives in the test are increasingly recognized.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhat is New:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study describes a previously unreported cause of a false positive sweat test. Three patients with homozygous mutations in the connexin 30 gene are described. All of them had an abnormal sweat test, and two of them presented with severe hyponatremic dehydration.\u003c/p\u003e"},{"header":"INTRODUCTION","content":"\u003cp\u003eThe \u003cb\u003esweat test (ST)\u003c/b\u003e consists of a measurement of sweat chloride concentration and conductivity in a sample of sweat. The test is mainly used as the gold standard for the diagnosis of cystic fibrosis (CF). CF is the most common life-threatening autosomal recessive disease in the Caucasian population, due to a multisystem disorder caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR), which encodes a chloride channel[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. When a patient presents a positive newborn screen, clinical symptomatology suggesting CF, or a positive family history, a diagnosis of CF can be made if the ST is pathological. An ST showing a chloride concentration greater than 60 mmol/L is considered as pathological; values between 30 and 60 mmol/L, as borderline results; whereas values less than 30 mmol/L are considered as normal ones [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHowever, there are several reports in the literature regarding conditions that are known to be associated with false positive or false negative ST results. The list of these conditions has grown significantly over time. Some examples include malnutrition, some metabolic disorders (such as mucopolysaccharidosis, type I fucosidosis or glycogen storage diseases), dermatological diseases (as congenital ectodermal dysplasia or atopic dermatitis), various endocrine disorders (e.g: panhypopituitarism, Addison disease, isolated adrenocorticoid deficiency, vasopressin-resistant diabetes insipidus, hypothyroidism and hypoparathyroidism) and carbonic anhydrase XII mutations [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e],[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn this article, we describe a previously unreported cause of false-positive ST: we identified three patients with a mutation in both alleles of the Gap Junction Beta (\u003cem\u003eGJB\u003c/em\u003e) 6 gene (encoding connexin 30, which is responsible for hearing impairment) in which no other potential causes of a positive result were found.\u003c/p\u003e \u003cp\u003eHearing impairment is a disabling disease with the highest rate of age-standardized disability worldwide. Globally, the prevalence of congenital hearing impairment is 1\u0026ndash;3 in 1000 children at birth or during early childhood [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Nonsyndromic hearing impairment (NSHI) is the most common form of neurosensory deafness, accounting for almost 70% of inherited hearing impairments. The majority of NHSI cases have an autosomal recessive pattern of inheritance [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe connexin gene family is the most prevalent gene that contributes to NSHI. Studies in European and Asian populations have identified pathogenic variants in \u003cem\u003eGJB2\u003c/em\u003e (encoding connexin 26) and \u003cem\u003eGJB6\u003c/em\u003e (encoding connexin 30) as the major contributors to autosomal recessive NSHI (ARNSHI). GJB2-c35delG is the most prevalent variant (20\u0026ndash;50%) found in cases of ARNSHI. The GJB6-D13S1830 deletion was identified in up to 9.7% of cases and thus is the second-largest contributor to the genetic etiology of NSHI in European populations, either with homozygous presentation or when present in addition to a \u003cem\u003eGJB2\u003c/em\u003e mutation on the opposite allele [\u003cspan additionalcitationids=\"CR7 CR8 CR9\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u0026ndash;[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eConnexins are a multigene family of at least 20 distinct integral membrane proteins in humans that are expressed throughout the body in overlapping and unique patterns. Six connexins can form a connexon, a specialized intracellular structure surrounding a pore. Two connexons in opposing cell membranes can align to form an intercellular gap junction. Gap junctions are aqueous intercellular channels that are found in all tissues of the human body, including skin, nervous tissue, cochlea, heart, and muscle [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eBy connecting neighboring cells together, gap junctions allow direct cell-to-cell communication via the rapid transfer of physiological signals, ions, water, and small nutrients, which is pivotal for the coordination and synchronization of cellular responses to internal and external stimuli. In recent years, mutations in the skin-expressed connexin genes \u003cem\u003eGJB2\u003c/em\u003e (connexin 26), GJB3, \u003cem\u003eGJB4\u003c/em\u003e (connexin 31 and 30.3), \u003cem\u003eGJB6\u003c/em\u003e (connexin 30), and Gap Junction Alpha 1 (connexin 43) have been linked to human hereditary diseases affecting both the epidermis and cochlea [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e"},{"header":"MATERIAL AND METHODS","content":"\u003cp\u003eThis was an observational, cross-sectional single-center study.\u003c/p\u003e \u003cp\u003eThe first case was a 22-month-old female child with neurosensory deafness due to a mutation in homozygosity of both \u003cem\u003eGJB6\u003c/em\u003e alleles. She required multiple admissions due to hyponatremic dehydration. In this context, a ST was performed as part of the study of recurrent hyponatremia, which was positive. CF was ruled out since she did not present other symptoms compatible with CF, her neonatal screening was negative and she had a genetic test with no mutations in CFTR.\u003c/p\u003e \u003cp\u003eFour months later, a 13-month-old female child with neurosensory deafness due to a mutation in the compound heterozygosity of both \u003cem\u003eGJB6\u003c/em\u003e alleles was also admitted due to a hyponatremic dehydration. Considering the previous case, a ST was also performed, resulting in a chloride concentration of 57 mmol/L. Similarly, no other symptoms of CF were observed and no mutations were detected in the CFTR gene.\u003c/p\u003e \u003cp\u003eFollowing these findings, the hospital\u0026rsquo;s genetic database was accessed in order to search for other patients with neurosensory deafness caused by a mutation in homozygosity or compound heterozygosity for connexin 30. Although no other pediatric patients were found, we identified an adult man with deafness with a mutation in the compound heterozygosity of both \u003cem\u003eGJB6\u003c/em\u003e alleles (third case). This patient was examined in 2009 as part of a genetic study of his daughters, who also have deafness.\u003c/p\u003e \u003cp\u003eThe first-degree relatives of these three patients with hearing impairment due to a mutation in both \u003cem\u003eGJB6\u003c/em\u003e alleles were also included. Informed consent was obtained from each participant. This study was approved by the Hospital Sant Joan de D\u0026eacute;u Ethics Committee (Esplugues, Spain, refPIC-115-24) and was done in accordance with the Declaration of Helsinki. Informed consent was obtained from the individual participants included in the study or their parents.\u003c/p\u003e \u003cp\u003eA ST was performed in all the selected cases. ST is a noninvasive test that is used for the determination of chloride in sweat. The first part of the test involves iontophoresis. In our center, it is performed with the Webster Sweat Inducer\u0026ndash;Wescor\u0026reg; system. Two electrodes (anode and cathode) with one disk each of pilocarpine (Pilogel\u0026reg;) are placed on the cleaned skin of the anterior part of the forearm. After 5 minutes of stimulation, the discs are removed and the skin surface is cleaned again. Immediately, the Macroduct\u0026reg; system collector is fixed. This is made up of a 0.6 mm capillary in diameter arranged in a spiral shape in a concave plastic disc with a central opening to collect sweat, which turns blue as it fills, to making it easier to see the amount collected. The required sample volume is 20\u0026ndash;50 \u0026micro;l, which is collected for a minimum period of 20 minutes and a maximum of 30 minutes. After the sample is detected to be sufficient, the collector is removed from the forearm and is immediately manipulated by the CF nurse to determine conductivity via Sweat-Check 3120, Wescor\u0026reg; and chlorodimetry via Chloride Analyzer 926, Sherwood Scientific Ltd. Prior to every intervention, the corresponding quality control was carried out with the Macroduct \u0026reg; system equipment.\u003c/p\u003e \u003cp\u003eIn cases 1 and 2, genetic tests were performed in order to rule out mutations in CFTR gene. Initially Elucigene CF-EU2 kit test was done. Then, a direct sequencing of the coding region of the gene was performed. In addition, deletions/duplications of the CFTR gene were analyzed by Multiplex Ligation-dependent Probe Amplification (MLPA) using the SALSA MLPA P091D2 kit (MRC Holland\u0026reg;). The results were obtained in an automatic sequencer ABI3130. This technique detects more than 99% of mutations in the CFTR gene [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. On the other hand, deletions in the \u003cem\u003eGJB6\u003c/em\u003e gene were obtained by using the SALSA MLPA P163-GJB-WFS1-POU3F4 kit (MRC Holland\u0026reg;), and analyzed with the Coffalyser program.\u003c/p\u003e \u003cp\u003eThe Mann-Whitney U test was used to compare medians between groups of patients. The statistical analysis was performed via SPSS v.24, with statistical significance defined as a p-value of \u0026lt;\u0026thinsp;0.05.\u003c/p\u003e"},{"header":"RESULTS","content":"\u003cp\u003eWe recruited three patients with a neurosensory deafness caused by a mutation in both alleles of connexin 30. A ST was also performed in their five relatives with deafness caused by other mutations. The results are described in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Among the three patients with a deletion in compound heterozygosis of connexin 30, two had a positive ST, whereas the third patient had a close-to-positivity borderline result (57 mmol/L). Moreover, there were no positive sweat tests in individuals with other mutation patterns. Patients with a deletion in both connexin 30 alleles presented increased chloride concentrations (p-value: 0.036) and conductivity (p-value: 0.035).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDescriptive features of patients with deafness in which a ST was performed.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003ePatient\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eIndex case\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eAge\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSex\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eMutation pattern\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c8\" namest=\"c6\"\u003e \u003cp\u003eSweat test\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eChloride\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eConductivity\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eInterpretation\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCase 1\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e22 months\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFemale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eGJB6\u003c/em\u003e homozygosis:\u003c/p\u003e \u003cp\u003e[del(GJB6-D13S1830)]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e67 mmol/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e80 mmol/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eAbnormal\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCase 2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13 months\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFemale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eGJB6\u003c/em\u003e compound heterozygosis:\u003c/p\u003e \u003cp\u003e[del(\u003cb\u003eGJB6\u003c/b\u003e-D13S18\u003cb\u003e30\u003c/b\u003e)\u0026thinsp;+\u0026thinsp;del(\u003cb\u003eGJB6\u003c/b\u003e-D13S18\u003cb\u003e54\u003c/b\u003e)]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e57 mmol/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e67 mmol/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eBorder-line\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCase 3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e48 years\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eGJB6\u003c/em\u003e compound heterozygosis:\u003c/p\u003e \u003cp\u003e[del(GJB6-D13S1854)\u0026thinsp;+\u0026thinsp;del(GJB6-D13S1830)]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e65 mmol/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e86 mmol/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eAbnormal\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCase 4\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCase 1 brother\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5 years\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eGJB6\u003c/em\u003e/\u003cem\u003eGJB2\u003c/em\u003e in heterozygosis:\u003c/p\u003e \u003cp\u003e[del(\u003cb\u003eGJB6\u003c/b\u003e-D13S1830)\u0026thinsp;+\u0026thinsp;\u003cb\u003eGJB2\u003c/b\u003e-c.35delG]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e10 mmol/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e44 mmol/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eNormal\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCase 5\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCase 1 father\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e35 years\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eGJB6\u003c/em\u003e/\u003cem\u003eGJB2\u003c/em\u003e in heterozygosis:\u003c/p\u003e \u003cp\u003e[del(\u003cb\u003eGJB6\u003c/b\u003e-D13S1830)\u0026thinsp;+\u0026thinsp;\u003cb\u003eGJB2\u003c/b\u003e-c.35delG]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e23 mmol/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e46 mmol/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eNormal\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCase 6\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCase 1 mother\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e38 years\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFemale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eGJB6\u003c/em\u003e/\u003cem\u003eGJB2\u003c/em\u003e in heterozygosis:\u003c/p\u003e \u003cp\u003e[del(\u003cb\u003eGJB6\u003c/b\u003e-D13S1830)\u0026thinsp;+\u0026thinsp;\u003cb\u003eGJB2\u003c/b\u003e-c.35delG]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e12 mmol/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e45 mmol/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eNormal\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCase 7\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCase 3 daughter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14 years\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFemale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eGJB6\u003c/em\u003e heterozygosity: [del(GJB6-D13S1854)]\u0026thinsp;+\u0026thinsp;unknown mutation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e20 mmol/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e43 mmol/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eNormal\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCase 8\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCase 3 daughter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14 years\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFemale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eGJB6\u003c/em\u003e heterozygosity: [del(GJB6-D13S1854)]\u0026thinsp;+\u0026thinsp;unknown mutation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e25 mmol/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e45 mmol/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eNormal\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003ePatient 1 is a 22-month-old female child with severe hearing impairment due to a mutation in homozygosis of both \u003cem\u003eGJB6\u003c/em\u003e alleles [del(GJB6-D13S1830)]. She is a bilateral cochlear implant recipient. Both the patient\u0026rsquo;s parents and her brother (cases 4\u0026ndash;6) experienced hearing impairment due to combination of a mutation in the heterozygosity of \u003cem\u003eGJB2\u003c/em\u003e [(GJB2-c.35delG)] and \u003cem\u003eGJB6\u003c/em\u003e [del(GJB6-D13S1830)].\u003c/p\u003e \u003cp\u003eThe patient visited the emergency department for vomiting, diarrhea and fever for 48 hours. A blood test revealed metabolic acidosis (pH 7.31, pCO2 30.5 mmHg, bicarbonate concentration 14.9 mmol/L) with a normal ionogram (sodium 136 mmol/L, potassium 4.2 mmol/L, chloride 106 mmol/L) and no increase in acute-phase reactants. Intravenous rehydration was started and the patient was admitted.\u003c/p\u003e \u003cp\u003eDuring hospitalization, a more thorough anamnesis revealed that she had been admitted four times in one year because of hyponatremia (up to 113 mmol/L), metabolic acidosis and dehydration in the context of vomiting and diarrhea. Previously, additional studies revealed no impairments in sodium fractional excretion or in cortisol and renin levels. As part of the study, a ST was performed, which yielded a positive result (with a chloride concentration of 67 mmol/L and conductivity of 80 mmol/L). She was referred to the CF unit, where a new ST test was also positive. Moreover, a genetic test ruled out CF and carbonic anhydrase XII mutations. She never presented with respiratory symptoms or signs of pancreatic insufficiency. As part of the study, a sweat test was also performed on her parents and brother, who were negative (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePatient 2 is a 13-month-old child with severe neurosensory deafness due to a mutation in the compound heterozygosity of \u003cem\u003eGJB6\u003c/em\u003e [del(GJB6-D13S1830) and del(GJB6-D13S1854)] with no family history of deafness. Her father is a carrier in heterozygosity of the mutation del (GJB6-D13S1830) and her mother is a carrier in heterozygosity of the mutation del(GJB6-D13S1854).\u003c/p\u003e \u003cp\u003eThe patient was admitted directly to the intensive care unit (ICU) due to hypovolemic shock caused by uncontrollable vomiting and refusal to eat for 12 hours in the context of high ambient temperature. Initially, a blood test revealed metabolic acidosis and hyponatremia of 120 mmol/L. During her stay in the ICU, she received inotropic drugs and aggressive rehydration. After the first stabilization in the ICU, she was transferred to the pediatric ward. Owing to a similar case (explained above) that presented with the same mutation, a ST was performed showing close-to-positivity results (chloride of 57 mmol/L and conductivity of 67 mmol/L). Moreover, a genetic test was performed and revealed no mutations related to cystic fibrosis. During 18 months of surveillance, she did not have any respiratory or gastrointestinal symptoms.\u003c/p\u003e \u003cp\u003ePatient 3 is a 48 year-old man with neurosensory deafness caused by a mutation in the compound heterozygosity of \u003cem\u003eGJB6\u003c/em\u003e [del(GJB6-D13S1830) and del(GJB6-D13S1854)] who had been studied in 2009 after having had twins with hearing impairment (cases 7\u0026ndash;8) due to a \u003cem\u003eGJB6\u003c/em\u003e mutation in heterozygosity. After observing the findings explained above, patient was recruited and a ST was performed, showing a positive result (chloride of 65 mmol/L and conductivity of 86 mmol/L). A thorough anamnesis was performed, and the patient had not experienced episodes of previous dehydration or respiratory or gastrointestinal symptoms. Since the patient was completely asymptomatic, and after observing the relationship between connexin 30 mutation and positive ST, a genetic test to rule out CF was not performed.\u003c/p\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eAs previously mentioned, connexins are expressed not only in the inner ear, but also in other tissues such as sweat glands and the epidermis. These molecules are assembled in order to form gap junctions, which allow the passage of small molecules between adjacent cells in animal tissues, coupling them electrically and metabolically. There are multiple types of connexins (such as 26, 30, 31 and 43). However, they tend to show overlapping expression patterns, and connexones formed by different types of connexins exist [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe ways in which connexins interact with each other and with other molecules are complex. They have paracrine actions, regulating, for instance, calcium and sodium channels [\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u0026ndash;[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. They also have mechanical functions, such as allowing the contraction of the myoepithelial cells of the sweat glands, thus enabling the excretion of sweat [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. This wide range of functions depends on subtle factors such as the position of the molecule on the cell surface or how they are placed in relation to other structures on which they exert their effect. Indeed, different types of mutations in connexin alleles affect how and where their molecules are expressed in the cells, as well as how they are transported within them [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. This translates into a great variability at the phenotypic level as well. For example, loss-of-function mutations are more related to nonsyndrome deafness, whereas gain-of-function mutations are described in diseases involving both skin and deafness. The G11R mutationin connexin 30, for instance, is related to Clouston syndrome (OMIM #129500), a type of ectodermal dysplasia that affects both hair, nails and skin [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. On the other hand, a wide variety of diseases involving connexin 26 have been described. Some of them are nonsyndromic, such as porokeratotic eccrine ostial and dermal duct nevus, in which nevi following a linear Blaschkoid pattern are observed. Many others are syndromic, showing an association between deafness and skin defects, such as keratitis ichthyosis deafness syndrome (OMIM #148210), or palmoplantar keratoderma associated with deafness (OMIM #148350).\u003c/p\u003e \u003cp\u003eAlthough connexins are also expressed in sweat glands, the literature concerning this phenomenon is scarce. In this sense, it is important to highlight a paper describing some patients with connexin 26-related genes [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The authors provided data suggesting that evolutionary balancing of monogenic disorders may be more frequent than presently thought by describing the association between sensory disorders caused by recessive mutations at the connexin 26 and skin alterations. They examined histology and \u003cem\u003ein vitro\u003c/em\u003e sweat production among members of families affected by R143W, a \u003cem\u003eGJB2\u003c/em\u003e mutation. They reported that both heterozygous and homozygous participants had a significantly thicker epidermis. Interestingly, only homozygotes presented relatively high concentrations of sodium and chloride in the sweat, which may be interpreted as a biological disadvantage.\u003c/p\u003e \u003cp\u003eThe reason why mutations in connexins could explain the relatively high concentrations of chloride and sodium in sweat is not clear. It is known that connexin 30 plays a role as a modulator of the activity of epithelial sodium channels (ENaC) via multiple pathways, such as the paracrine secretion of ATP or glutamate or the promotion of clathrin-mediated ENaC endocytosis [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. In relation to this fact, Sipos et al. observed that mice with connexin 30 deficiencies had a reduced natriuretic capacity in response to hypertension, as their ability to regulate sodium reabsorption was limited [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThese observations emphasize that connexins play a role in regulating sodium transport but would not justify a positivity in the ST. In this regard, the intrinsic actions of connexin 30 are particularly complex and are closely linked to the expression of connexin 26 in both inner ear and sweat glands. Therefore, it has been defined that deletions of the \u003cem\u003eGJB6\u003c/em\u003e gene directly affect the expression of connexin [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. More specifically, Common et al. showed a case of a deaf child with a del(GJB6-D13S1830) and GJB2-c.35delG constellation in which a skin biopsy was performed. The authors compared his biopsy results with those of a healthy control and a patient with a heterozygous mutation in the connexin 26 gene. They observed that the case patient, but not the others, showed a marked decrease in the expression of connexin 26 in the duct, but not in the excretory portion of the sweat gland, without affecting the expression of connexin 30 itself; as well as an alteration of keratin expression, which acts supporting many other molecules [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn conclusion, although unabnle to give a definitive explanation, we found that all patients with a mutation affecting both alleles of connexin 30 presented concentrations of chloride in sweat higher than 55 mEq/L. However, those patients with genetic deafness explained by other allelic constellations presented with normal ST.\u003c/p\u003e \u003cp\u003eIt should be emphasized that these results may be relevant from a clinical point of view. Patients with these mutations could be exposed to a greater risk of dehydration during the first months of life, especially during the hot months in warm countries. In fact, two of the patients in our series required hospital admission, even in the PICU.\u003c/p\u003e \u003cp\u003eTo the best of our knowledge, this is the first study in which a mutation in connexin 30 has been described as a possible explanation for the positivity of a ST in patients with severe deafness. The most important limitation of our study is the small sample size. This limitation is justified by the low incidence of mutations affecting connexin 30 in our country. In this sense, we think that a multicenter study should be performed to confirm this relationship.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cul\u003e\n \u003cli\u003eARNSHI: autosomal recessive NSHI.\u003c/li\u003e\n \u003cli\u003eCF: cystic fibrosis.\u003c/li\u003e\n \u003cli\u003eCFTR: cystic fibrosis transmembrane conductance regulator.\u003c/li\u003e\n \u003cli\u003eENaC: epithelial sodium channels.\u003c/li\u003e\n \u003cli\u003e\u003cem\u003eGJB\u003c/em\u003e: Gap junction beta\u003c/li\u003e\n \u003cli\u003eICU: Intensive Care Unit\u003c/li\u003e\n \u003cli\u003eMLPA: multiplex ligation-dependent probe amplification.\u003c/li\u003e\n \u003cli\u003eNSHI: nonsyndromic hearing impariment.\u003c/li\u003e\n \u003cli\u003eST: sweat test.\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding\u003c/h2\u003e\n\u003cp\u003eThe authors declare that no funds, grants, or other support were received during the preparation of this manuscript.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eAnna Rossell: ARAleix Soler-Garc\u0026iacute;a: ASLoreto Martorell: LMAnt\u0026ograve;nia Claveria: ACLaura Valero: LVS\u0026iacute;lvia Rodr\u0026iacute;guez: SRC\u0026egrave;lia Badenas: CBMaria Cols-Roig: MCAll authors contributed to the study conception and design. Data collection was performed by AR and AS. Material preparation and analysis were performed by AR, AS, LM and MC. Clinical and laboratory tests were performed by SR, LM and CB. A deep critical review was performed by CB, LV and AC. The first draft of the manuscript was written by AR and all authors commented on previous versions of the manuscript. All authors read and approved the fnal manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eFarrell PM, White TB, Ren CL, et al. Diagnosis of Cystic Fibrosis: Consensus Guidelines from the Cystic Fibrosis Foundation. \u003cem\u003eJ Pediatr\u003c/em\u003e. 2017;181S:S4-S15.e1. \u003c/li\u003e\n\u003cli\u003eTurcios NL. Cystic Fibrosis Lung Disease: An Overview. \u003cem\u003eRespir Care\u003c/em\u003e. 2020;65(2):233-251. \u003c/li\u003e\n\u003cli\u003eFeldshtein M, Elkrinawi S, Yerushalmi B, et al. Hyperchlorhidrosis caused by homozygous mutation in CA12, encoding carbonic anhydrase XII. \u003cem\u003eAm J Hum Genet\u003c/em\u003e. 2010;87(5):713-720. \u003c/li\u003e\n\u003cli\u003eGuglani L, Stabel D, Weiner DJ. False-Positive and False-Negative Sweat Tests: Systematic Review of the Evidence. \u003cem\u003ePediatr Allergy Immunol Pulmonol\u003c/em\u003e. 2015;28(4):198-211. \u003c/li\u003e\n\u003cli\u003eMehra S, Eavey RD, Keamy DG. The epidemiology of hearing impairment in the United States: newborns, children, and adolescents. \u003cem\u003eOtolaryngol Head Neck Surg\u003c/em\u003e. 2009;140(4):461-472. \u003c/li\u003e\n\u003cli\u003eSnoeckx RL, Huygen PLM, Feldmann D, et al. GJB2 mutations and degree of hearing loss: a multicenter study. \u003cem\u003eAm J Hum Genet\u003c/em\u003e. 2005;77(6):945-957. \u003c/li\u003e\n\u003cli\u003eDel Castillo FJ, Rodr\u0026iacute;guez-Ballesteros M, \u0026Aacute;lvarez A, et al. A novel deletion involving the connexin-30 gene, del(GJB6-d13s1854), found in trans with mutations in the GJB2 gene (connexin-26) in subjects with DFNB1 non-syndromic hearing impairment. \u003cem\u003eJ Med Genet\u003c/em\u003e. 2005;42(7):588-594. \u003c/li\u003e\n\u003cli\u003eWonkam ET, Chimusa E, Noubiap JJ, Adadey SM, Fokouo JVF, Wonkam A. GJB2 and GJB6 Mutations in Hereditary Recessive Non-Syndromic Hearing Impairment in Cameroon. \u003cem\u003eGenes (Basel)\u003c/em\u003e. 2019;10(11). \u003c/li\u003e\n\u003cli\u003eMarlin S, Feldmann D, Blons H, et al. GJB2 and GJB6 mutations: genotypic and phenotypic correlations in a large cohort of hearing-impaired patients. \u003cem\u003eArch Otolaryngol Head Neck Surg\u003c/em\u003e. 2005;131(6):481-487.\u003c/li\u003e\n\u003cli\u003ePandya A, O\u0026rsquo;Brien A, Kovasala M, Bademci G, Tekin M, Arnos KS. Analyses of del(GJB6-D13S1830) and del(GJB6-D13S1834) deletions in a large cohort with hearing loss: Caveats to interpretation of molecular test results in multiplex families. \u003cem\u003eMol Genet genomic Med\u003c/em\u003e. 2020;8(4). \u003c/li\u003e\n\u003cli\u003eAvshalumova L, Fabrikant J, Koriakos A. Overview of skin diseases linked to connexin gene mutations. \u003cem\u003eInt J Dermatol\u003c/em\u003e. 2014;53(2):192-205. \u003c/li\u003e\n\u003cli\u003eSavant A, Lyman B, Bojanowski C, et al. Cystic Fibrosis. \u003cem\u003ePediatr Pulmonol\u003c/em\u003e. 1993;58(11):3013-3022. \u003c/li\u003e\n\u003cli\u003eLilly E, Sellitto C, Milstone LM, White TW. Connexin channels in congenital skin disorders. \u003cem\u003eSemin Cell Dev Biol\u003c/em\u003e. 2016;50:4-12. \u003c/li\u003e\n\u003cli\u003eRichard G. Connexin disorders of the skin. \u003cem\u003eClin Dermatol\u003c/em\u003e. 2005;23(1):23-32. \u003c/li\u003e\n\u003cli\u003eSipos A, Vargas SL, Toma I, Hanner F, Willecke K, Peti-Peterdi J. Connexin 30 deficiency impairs renal tubular ATP release and pressure natriuresis. \u003cem\u003eJ Am Soc Nephrol\u003c/em\u003e. 2009;20(8):1724-1732. \u003c/li\u003e\n\u003cli\u003eNakashima K, Kato H, Kurata R, et al. Gap junction-mediated contraction of myoepithelial cells induces the peristaltic transport of sweat in human eccrine glands. \u003cem\u003eCommun Biol\u003c/em\u003e. 2023;6(1). \u003c/li\u003e\n\u003cli\u003eKutkowska-Kaźmierczak A, Niepok\u0026oacute;j K, Wertheim-Tysarowska K, et al. Phenotypic variability in gap junction syndromic skin disorders: experience from KID and Clouston syndromes\u0026rsquo; clinical diagnostics. \u003cem\u003eJ Appl Genet\u003c/em\u003e. 2015;56(3):329-337. \u003c/li\u003e\n\u003cli\u003eMeyer CG, Amedofu GK, Brandner JM, Pohland D, Timmann C, Horstmann RD. Selection for deafness? \u003cem\u003eNat Med\u003c/em\u003e. 2002;8(12):1332-1333. \u003c/li\u003e\n\u003cli\u003eIlyaskin A V., Korbmacher C, Diakov A. Inhibition of the epithelial sodium channel (ENaC) by connexin 30 involves stimulation of clathrin-mediated endocytosis. \u003cem\u003eJ Biol Chem\u003c/em\u003e. 2021;296. \u003c/li\u003e\n\u003cli\u003eRodriguez-Paris J, Tamayo ML, Gelvez N, Schrijver I. Allele-specific impairment of GJB2 expression by GJB6 deletion del(GJB6-D13S1854). \u003cem\u003ePLoS One\u003c/em\u003e. 2011;6(6). \u003c/li\u003e\n\u003cli\u003eCommon JEA, Bitner-Glindzicz M, O\u0026rsquo;Toole EA, et al. Specific loss of connexin 26 expression in ductal sweat gland epithelium associated with the deletion mutation del(GJB6-D13S1830). \u003cem\u003eClin Exp Dermatol\u003c/em\u003e. 2005;30(6):688-693.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"european-journal-of-pediatrics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ejpe","sideBox":"Learn more about [European Journal of Pediatrics](https://www.springer.com/journal/431)","snPcode":"431","submissionUrl":"https://submission.nature.com/new-submission/431/3","title":"European Journal of Pediatrics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"sweat test, connexin 30, GJB6 and neurosensory deafness","lastPublishedDoi":"10.21203/rs.3.rs-6213266/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6213266/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003ePurpose\u003c/strong\u003e: The sweat test is the gold standard for the diagnosis of cystic fibrosis. There are several reports in the literature regarding conditions that are known to be associated with a false positive result. In aim of this article is describing a previously unreported cause of a false positive sweat test (ST).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods\u003c/strong\u003e: An observational, cross-sectional single-center study was performed. We recruited three patients with a neurosensory deafness caused by a deletion in both alleles of connexin 30. The first-degree relatives of these three patients with hearing impairment due to other mutations were also included. A ST was performed in all the selected cases.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003c/strong\u003e: Among the three patients with a deletion in both connexin 30 alleles, two had a positive ST, whereas the third patient had a close-to-positivity borderline result (57 mmol/L). Moreover, there were no positive sweat tests in individuals with other mutation patterns.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion\u003c/strong\u003e: Patients with affection of both alleles of connexin 30 were the only ones to show a positive ST, which may translate a higher risk of hyponatremic dehydration. The reason of the ST positivity remains unclear and may be related to the fact that connexin 30 plays a role modulating other molecules in both inner ear and sweat glands.\u003c/p\u003e","manuscriptTitle":"Connexin 30 (GJB6) deletion as a cause of a false positive sweat test result","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-03-27 12:22:43","doi":"10.21203/rs.3.rs-6213266/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-04-13T16:32:26+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-13T14:31:58+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-01T13:19:19+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"193849008420933451840941471075626039529","date":"2025-03-20T10:34:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"118948112550935150221247651265959968443","date":"2025-03-19T08:06:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"247088375111917707284593166163312905142","date":"2025-03-18T23:30:30+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-03-18T07:21:40+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-03-18T00:11:53+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-03-17T23:35:45+00:00","index":"","fulltext":""},{"type":"submitted","content":"European Journal of Pediatrics","date":"2025-03-12T15:03:21+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"european-journal-of-pediatrics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ejpe","sideBox":"Learn more about [European Journal of Pediatrics](https://www.springer.com/journal/431)","snPcode":"431","submissionUrl":"https://submission.nature.com/new-submission/431/3","title":"European Journal of Pediatrics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"a08a57bd-c315-4266-9004-2592987a873a","owner":[],"postedDate":"March 27th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-06-16T15:59:05+00:00","versionOfRecord":{"articleIdentity":"rs-6213266","link":"https://doi.org/10.1007/s00431-025-06220-7","journal":{"identity":"european-journal-of-pediatrics","isVorOnly":false,"title":"European Journal of Pediatrics"},"publishedOn":"2025-06-12 15:57:03","publishedOnDateReadable":"June 12th, 2025"},"versionCreatedAt":"2025-03-27 12:22:43","video":"","vorDoi":"10.1007/s00431-025-06220-7","vorDoiUrl":"https://doi.org/10.1007/s00431-025-06220-7","workflowStages":[]},"version":"v1","identity":"rs-6213266","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6213266","identity":"rs-6213266","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}