Hartnup disease combined with iminocaciduria: two novel mutations in the SLC6A19 gene (a case report)

Hartnup disease combined with iminocaciduria: two novel mutations in the SLC6A19 gene (a case report) | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Case Report Hartnup disease combined with iminocaciduria: two novel mutations in the SLC6A19 gene (a case report) Ningning Mei, Lei Li, Yan Cui, Liang Wang, Hong Jiang, Xinying Tian This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5447826/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Purpose To report a case of Hartnup disease combined with iminocaciduria, and to explore its clinical manifestations and genetic mutations. Methods Clinical data of the patient were collected, whole-exome sequencing was performed using high-throughput sequencing technology to detect SLC6A19 gene mutations. Sanger sequencing was used for family verification, and software was employed to predict protein structure and function. Results The patient exhibited intermittent pellagra, ataxia, and psychiatric symptoms. Genetic sequencing revealed three heterozygous mutations in the SLC6A19 gene: a heterozygous missense mutation c.169C > T (p.Ary57Cys), a heterozygous missense mutation c.1802C > A (p.A601D), and a heterozygous splicing mutation c.1378 + 5G > A. The c.169C > T and c.1378 + 5G > A mutations were inherited from the father, whereas the mutation c.1802C > A was passed down from the mother. Bioinformatics-based protein function prediction indicated that both the c.169C > T (p.R57C) and c.1802C > A (p.A601D) mutations are harmful. Furthermore, the levels of 5-oxoproline and proline in the urine were elevated. Conclusion The typical manifestations of Hartnup disease include intermittent pellagra, ataxia, and psychiatric symptoms. The SLC6A19 mutations c.1802C > A and c.1378 + 5G > A are novel, and this case expands the genetic spectrum of the disease. Hartnup disease SLC6A19 gene Novel mutations iminocaciduria Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Hartnup disease is a rare autosomal recessive disease discovered in 1956 1 , characterized by neutral aminoaciduria, pellagra-like skin symptoms (including pigmentation and discoloration in sun-exposed areas), ataxia, and various psychiatric manifestations. The clinical features and course of the disease can be variable. However, aminoaciduria remains a persistent finding 2 .The etiology of the disease is attributed to a mutation in the SLC6A19 gene, which encodes the neutral amino acid transport protein. The incidence rate in the European population is approximately 1 in 30,000. This report presents a case of Hartnup disease combined with iminocaciduria, outlining clinical manifestations and pedigree analysis, with the aim of enhancing awareness of this condition. Case presentation The patient is a 34-year-old unmarried male who was admitted due to unsteady walking persisting for one year. The instability arose unexpectedly, characterized by a leftward tilt, intermittent limb tremors, and multiple falls. The patient demonstrated significant upper limb strength but no limb numbness or sensory abnormalities in his extremities. Medical history reveals that 23 years prior, the patient began to exhibit withdrawn and passive behavior, avoiding social interactions with peers and showing a lack of response to those around him. He spoke softly and often lowered his head. Eleven years ago, upon entering the workforce, he developed heightened sensitivity and suspicion, remaining perpetually on edge and frequently glancing around anxiously. A year ago, due to his pronounced sensitivity and behavioral abnormalities, he was diagnosed with schizophrenia at another hospital. Additionally, the patient experiences “photosensitivity,” evident by rough, pigmented skin on sun-exposed areas such as the hands and face during the summer months, with improvement noted by the season's end. There is no reported history of birth injuries or asphyxia, and there is no similar family history; his parents are not closely related. Upon physical examination at the time of admission: diffuse brown spots with slightly rough surfaces and a few fine, fragmented scales were observed on the backs of both hands (Fig. 1A). Brownish-yellow patches with well-defined borders are noted on the forehead and face (Fig. 1B). The right toenail exhibited atrophy and thinning, accompanied by a rough surface (Fig. 1C). Neurological examination revealed that the patient was alert and articulates clearly, albeit demonstrating sluggish reactions without significant memory deficits. Small, intermittent horizontal nystagmus was noted. Muscle strength assessment showed 4 + in the proximal lower limbs and 5 in the distal lower limbs. Increased muscle tone was observed in the right lower limb, presenting a “knife-like” appearance. Upper limb tendon reflexeswere intact, while lower limb tendon reflexes were markedly exaggerated (+++++). Both Babinski's signs were positive. No notable abnormalities were detected during the sensory system evaluation. In the coordination assessment, the right-sided finger-to-nose test was unstable and inaccurate. No neck stiffness was noted. There was no significant delay in bilateral finger-to-finger or fist clenching. No tremors or involuntary movements were observed. Gait analysis reveaed an abnormal pattern characterized by a wide base, threshold-crossing gait, and impaired tandem gait. Laboratory tests, including routine assessments of blood, urine, and stool tests, as well as evaluations of myocardial enzymes, electrolytes, liver and kidney function, thyroid function, and D-dimer levels, revealed no significant abnormalities. Cerebrospinal fluid (CSF) analyses, encompassing both routine and biochemical tests, were within normal limits. Additionally, tests for autoantibodies, autoimmune encephalitis antibodies in both blood and CSF, and paraneoplastic antibodies returned negative results. An abdominal ultrasound yielded unremarkable findings. Cranial imaging: Diffusion-weighted imaging (DWI) and MRI of the brain revealed scattered ischemic lesions in the bilateral frontal lobes, right parietal lobe, and corona radiata, and the left insular lobe. No discernible diffusion-restricted signals were identified within the brain parenchyma. Electromyography (EMG) revealed damage to the motor fibers of the bilateral common peroneal nerves and tibial nerves, with "F" waves failing to elicite from the bilateral common peroneal nerves. A video electroencephalogram (EEG) demonstrated widespread θ theta slow wave activity. Cognitive screening yielded a Mini-Mental State Examination (MMSE) score of 26 and a Montreal Cognitive Assessment (MoCA) score of 24. Urinary organic acid analysis showed elevated levels of 5-oxoproline and proline. Blood tests for genetic metabolic disorders, including amino acid and acylcarnitine profiles, did not reveal any abnormalities in neutral amino acids. Genetic testing: With the patient's informed consent, whole exome sequencing was performed using venous blood samples (conducted by MyGenostics, Beijing). The results revealed three heterozygous mutations in the SLC6A19 gene: 1. Exon 1: A heterozygous mutation at nucleotide 169, where cytosine (C) is replaced by thymine (T) (c.169C > T), results in a missense mutation that changes the amino acid from arginine to cysteine at position 57 (p.R57C) (Fig. 2 A);2. Exon 12: A heterozygous mutation at nucleotide 1802, where cytosine (C) is replaced by adenine (A) (c.1802C > A), causes another missense mutation that changes the amino acid from alanine to aspartic acid at position 601 (p.A601D) (Fig. 2 B). 3. Exon 9: A heterozygous mutation at c.1378 + 5G > A, leading to a splicing mutation (Fig. 2 C). Pedigree verification by Sanger DNA sequencing revealed that the c.169C > T and c.1378 + 5G > A mutations were inherited from the father, while the c.1802C > A mutation was inherited from the mother. The family pedigree is shown in Fig. 2 . Protein model building and functional prediction: The wild-type 3D model of the SNCA gene was retrieved from the SWISS-MODEL database ( https://swissmodel.expasy.org/ ), identified as Q9D687.1.A and encompassing residues 1-633. This model displays a sequence similarity of 58% and a sequence identity of 86.89% indicating a high degree of relatedness to the template structure. The modeling quality, assessed by the GMQE score is 0.9, which suggests excellent model quality and strong consistency with experimentally determined structures. The homologous model data were visualized using PyMOL ( https://pymol.org/2/ ) 3–6 .Functional predictions were conducted for the mutations c.169C > T and c.1802C > A, aimed at assessing their potential impact on protein function and stability, the results are shown in Fig. 3 . For the SLC6A19 mutation NM_001003841 c.169C > T (p.R57C), the wild-type SLC6A19 protein features arginine (Arg, R) at position 57, which is replaced by cysteine (Cys, C) due to this mutation. After this mutation, the number and length of hydrogen bonds remain unchanged. Here are the potential effects of this substitution on the protein: 1.Charge Change: Arginine has a positive charge, while cysteine has a neutral thiol group. This change can significantly alter the protein’s charge distribution, potentially affecting its interactions with other molecules. 2. Polarity Change: Cysteine has weaker polarity compared to arginine, which might impact the protein's solubility and stability (Fig. 3 A). For the SLC6A19 mutation NM_001003841 c.1802C > A (p.A601D) mutation, the wild-type SLC6A19 protein features alanine (Ala, A) at position 601, which is replaced by aspartic acid (Asp, D) due to this mutation. The number and length of hydrogen bonds remain unchanged after the mutation. Here are the potential effects of this substitution on the protein: 1. Charge Change: Alanine is neutral, while aspartic acid carries a negative charge. This substitution may alter the protein's charge distribution, potentially affecting its interactions with other molecules. 2. Polarity Change: Alanine is non-polar, whereas aspartic acid is polar. The introduction of a polar side chain in place of a non-polar side chain may influence the protein's solubility, stability, and overall conformation. 3. Conformational Flexibility: Alanine's short, non-polar side chain usually generally contributes to greater flexibility in the protein structure, while aspartic acid's polar side chain may restrict this flexibility, affect the protein's dynamics and conformational changes necessary for its function (Fig. 3 B). Bioinformatics Analysis: By comparing the differences in amino acid sequences of the mutations with those of other animals using database resources, multiplex sequence alignment results showed that the SLC6A19 protein had an Arg(R) at amino acids 57 and Ala(A) at amino acids 601, which are conserved across multiple mammals, including humans (Fig. 4 , indicated by red arrows). Specifically, position 57 is arginine (Arg, R) and position 601 is alanine (Ala, A).Using comprehensive bioinformatics protein function prediction tools such as REVEL, SIFT, PolyPhen_2, MutationTaster, and GERP, the predictions for the c.169C > T (p.R57C) and c.1802C > A (p.A601D) mutations indicate that both mutations are likely harmful. This suggests that they may disrupt the normal function of the SLC6A19 protein, potentially contributing to pathologies associated with its dysfunction, such as Hartnup disorder or other related conditions. A heterozygous mutation at c.1378 + 5G > A, leading to a splicing mutation, may affect the normal splicing of the pre-mRNA, potentially resulting in an incorrect or truncated protein product. Treatment: The patient received intravenous niacin treatment followed by a prescription for oral extended-release niacin tablets (0.5 g) to be taken once daily at night after discharge. The patient's rash improved, and his mental state and mood restored to a normal level. This indicates a positive response to niacin treatment. Discussion The classic clinical manifestations of Hartnup disease include intermittent pellagra-like dermatitis (rashes), cerebellar ataxia, and psychiatric symptoms 7 . In this case, the patient exhibited withdrawn and passive behavior from an early age, and gradually developed psychiatric symptoms including heightened sensitivity and anxiety. He was hospitalized for schizophrenia and exhibited mild cognitive impairment, along with progressive symptoms such as unsteady walking, tremors, frequent falls, and impaired coordination. Photosensitive pellagra-like changes were observed on the skin of the patient's hands and face, which are consistent with the clinical features of Hartnup disease. Using high-throughput and Sanger sequencing, three mutation sites in the SLC6A19 gene were identified: two heterozygous missense mutations of c.1802C > A and c.169C > T, and a heterozygous splicing mutation of c.1378 + 5G > A. The patient, possessing compound heterozygous mutations, was ultimately diagnosed with Hartnup disease. In 2004, the causative gene for Hartnup disease was cloned and identified as the SLC6A19 gene located on chromosome 5p15 8 . This gene encodes a sodium- and chloride-dependent neutral amino acid transporter B0AT1, which is primarily expressed in the kidney and small intestine. B0AT1 serves as a critical transporter responsible for over 95% of the absorption of free neutral amino acids in the small intestine and their subsequent reabsorption in the kidney 9 . The metabolic defect in Hartnup disease arises from the dysfunction of the neutral amino acid transporter, resulting in excessive loss of various amino acids in urine. A key issue is the impaired transport of tryptophan, which disrupts the disruption of the tryptophan-kynurenine-niacinamide metabolic pathway. This impairment results in reduced tryptophan absorption and increased production of indole, inhibiting niacin synthesis and causing niacin deficiency. Niacin deficiency can manifest as pellagra-like skin rashes and neurological damage. Pellagra-like rashes may either spontaneously resolve or improve following niacin treatment and typically present as photosensitive dermatitis 10 . Neurological symptoms associated with Hartnup disease encompass episodic ataxia, behavioral disturbances, and psychiatric issues such as anxiety, depression, and mild intellectual disability 7 . Additional potential symptoms include tremors, seizures 11 , diplopia, spastic paraplegia, and peripheral neuropathy 7 .A case reported by Jiang Wei et al. 12 showed that the levels of neutral amino acids in the urine of a proband were significantly elevated above standard values, indicating that mutations in the SLC6A19 gene lead to neutral amino acid transport disorders and hyperaminoaciduria. A limitation of this case is the absence of urinary neutral amino acid levels testing for the patient, and future assessments could further validate the metabolic alterations associated with this condition. The father of the patient in this case has two mutation sites, namely c.169C > T (p.Ary57Cys) and c.1378 + 5G > A. The mutation c.169C > T has been reported as a pathogenic mutation 8 . However, there are no relevant reports in the literature database regarding c.1802C > A and c.1378 + 5G > A, suggesting that these are novel mutations. The SLC6A19 gene comprises 12 exons, and it has been reported that specific mutations in exons 1, 6, and 12 may severely impair the function of the B0AT1 transporter, leading to noticeable clinical manifestations of Hartnup disease. Conversely, other mutations may cause aminoaciduria without presenting any symptoms 10 , 13 . Mutations located within the transmembrane domains of the SLC6A19 transporter can result in dysfunction of the protein, leading to pronounced neutral aminoaciduria, skin issues, and neurological symptoms. In contrast, mutations outside of the transmembrane domains, however, may only partially affect the transporter's function 14 , resulting in milder clinical manifestations. According to the topological model of human SLC6A19 described by Bröer S 15 , the mutations c.169C > T (p.Arg57Cys) and c.1802C > A (p.A601D) are located in the transmembrane regions of exons 1 and 12, respectively. Therefore, these mutations are likely to cause transporter dysfunction and lead to clinical symptoms. Additionally, our protein modeling and prediction results indicate that the mutations at these two sites are pathogenic, further reinforcing this conclusion. However, experimental studies may be required to characterize these changes fully and understand their biological significance, especially in the context of disorders associated with SLC6A19 dysfunction. The SLC6A19 gene plays a crucial role in the renal reabsorption of neutral amino acids. Mutations in SLC6A19 can also affect the transport of imino acids and glycine in the kidneys and intestines. This dysfunction may lead to conditions such as iminoglycinuria (IG) and hyperglycinuria (HG) 16 . In the kidneys, the transport of proline and glycine is mediated by four transport proteins: SLC36A2 (PAT2): Proline and glycine transporter, SLC6A18 (B0AT3 or XT2): Glycine transporter,SLC6A19 (B0AT1): Neutral amino acid transporter, SLC6A20 (IMINO or SIT1): Proline-specific transporter 16 , 17 .The main genes associated with iminoglycinuria and hyperglycinuria are SLC36A2 and SLC6A20. Genetic variations in SLC6A18 or SLC6A19 alone are generally insufficient to cause iminoglycinuria or hyperglycinuria 18 . In humans, the kidneys exhibit a stronger capacity for proline reabsorption compared to glycine, with most proline reabsorption being mediated by SLC36A2. Iminoglycinuria is inherited in an autosomal recessive manner and is characterized by increased excretion of proline and glycine in the urine. Both Iminoglycinuria and hyperglycinuria can present with a range of symptoms including hypertension, diabetes, kidney stones, intellectual disability, atypical chorioretinal atrophy, hearing loss, and blindness 19 .Hyperglycinuria is generally the result of defects in glycine metabolism or abnormalities in the renal tubular reabsorption of glycine. Excessive glycine levels can lead to elevated oxalate levels, as glycine is involved in the metabolic pathways that generate oxalate. Defects in oxalate transport can result in increased urinary oxalate content which may cause damage to renal tubular epithelial cells. This damage can promote the formation of calcium oxalate stones. Pan et al. 20 reported a case of a young male patient from China with hyperglycinuria attributed to the SLC6A19 c.1278C > T (p.Cys426) mutation, this patient ultimately exhibited bilateral calcium oxalate kidney stones. Mutations in the SLC6A19 gene can lead to impaired renal reabsorption of amino acids and disrupt the transport of related metabolites. Although SLC6A19 is also involved in the transport of proline and glycine, Hartnup disease is characterized by the excretion of all neutral amino acids, except for proline, in the urine 19 . In this case, the patient exhibited typical symptoms of Hartnup disease, with elevated levels of 5-hydroxyproline in the urine. Although urinary glycine levels were not tested, the absence of kidney stones indicates that glycine transport function may not be significantly affected, distinguishing this case from generalized hyperglycinuria. Therefore, Hartnup disease with iminoglycinuria is considered. Iminoglycinuria refers to the excretion of imino acids, primarily proline and hydroxyproline, along with some neutral amino acids, which results from the impaired reabsorption mechanisms. In summary, Hartnup disease is a rare, treatable genetic metabolic disease characterized by intermittent pellagra-like dermatitis (rashes), cerebellar ataxia, psychiatric symptoms, and neutral aminoaciduria. Genetic testing is crucial for diagnosis. In this case, two novel mutation sites, c.1802C > A and c.1378 + 5G > A, were identified, thereby expanding the genetic spectrum associated with Hartnup disease. The diagnosis of Hartnup disease combined with iminoglycinuria provides a comprehensive understanding of the patient's condition. Abbreviations CSF Cerebrospinal fluid DWI Diffusion-weighted imaging MRI Magnetic resonance imaging EMG Electromyography EEG electroencephalogram MMSE Mini-Mental State Examination MoCA Montreal Cognitive Assessment IG iminoglycinuria HG hyperglycinuria. Declarations Ethics approval and consent to participate Not applicable. Consent for publication Written informed consent was obtained from the patient for publication of this case report and any accompanying images. Availability of data and materials All the data analysed during this study are included in this article. Competing interests The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Funding None. Acknowledgments The authors would like to thank the patient for their cooperation, their patience in providing the necessary information. Authors ’ contributions Ningning Mei: case report concept and design, data collection, drafting of the manuscript; Lei Li, Yan Cui, Liang Wang, Hong Jiang: patient’s clinical and paraclinical management; Xinying Tian: provided supervision and revised the manuscript. References BARON DN, DENT CE, HART HARRISH, JEPSON EW. 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Automated comparative protein structure modeling with SWISS-MODEL and Swiss-PdbViewer: a historical perspective. Electrophoresis. 2009;30(Suppl 1):S162–73. Wang X, Li XY, Piao Y, et al. Hartnup disease presenting as hereditary spastic paraplegia and severe peripheral neuropathy. Am J Med Genet A. 2022;188(1):237–42. Kleta R, Romeo E, Ristic Z, et al. Mutations in SLC6A19, encoding B0AT1, cause Hartnup disorder. Nat Genet. 2004;36(9):999–1002. Belanger AJ, Gefteas E, Przybylska M, et al. Excretion of excess nitrogen and increased survival by loss of SLC6A19 in a mouse model of ornithine transcarbamylase deficiency. J Inherit Metab Dis. 2023;46(1):55–65. Zheng Y, Zhou C, Huang Y, Bu D, Zhu X, Jiang W. A novel missense mutation in the SLC6A19 gene in a Chinese family with Hartnup disorder. Int J Dermatol. 2009;48(4):388–92. Cheon CK, Lee BH, Ko JM, Kim HJ, Yoo HW. Novel mutation in SLC6A19 causing late-onset seizures in Hartnup disorder. Pediatr Neurol. 2010;42(5):369–71. Wei Jiang S, Li C, Zhou Y, Huang, Dingfang PU, Xunjun, Zhu. Analysisofm utatiosin the SLC6A 19 gene in a Chinese family witIlH artnup disease. China J Lepr Skin Dis. 2009;25(12):877–9. Nozaki J, Dakeishi M, Ohura T, et al. Homozygosity mapping to chromosome 5p15 of a gene responsible for Hartnup disorder. Biochem Biophys Res Commun. 2001;284(2):255–60. Zhu Y, Chen L, He J, et al. Study of Seizure-Manifested Hartnup Disorder Case Induced By Novel Mutations in SLC6A19. Open Life Sci. 2018;13:22–7. Bröer S. The role of the neutral amino acid transporter B0AT1 (SLC6A19) in Hartnup disorder and protein nutrition. IUBMB Life. 2009;61(6):591–9. Bröer S, Bailey CG, Kowalczuk S, et al. Iminoglycinuria and hyperglycinuria are discrete human phenotypes resulting from complex mutations in proline and glycine transporters. J Clin Invest. 2008;118(12):3881–92. Vanslambrouck JM, Bröer A, Thavyogarajah T, et al. Renal imino acid and glycine transport system ontogeny and involvement in developmental iminoglycinuria. Biochem J. 2010;428(3):397–407. Kukułowicz J, Pietrzak-Lichwa K, Klimończyk K, Idlin N, Bajda M. The SLC6A15-SLC6A20 Neutral Amino Acid Transporter Subfamily: Functions, Diseases, and Their Therapeutic Relevance. Pharmacol Rev. 2023;76(1):142–93. Bröer A, Cavanaugh JA, Rasko JE, Bröer S. The molecular basis of neutral aminoacidurias. Pflugers Arch. 2006;451(4):511–7. Pan Y, Wang S, Liu L, Liu X. The SLC6A19 gene mutation in a young man with hyperglycinuria and nephrolithiasis: a case report and literature review. BMC Urol. 2022;22(1):190. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. 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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-5447826","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":380979496,"identity":"f5d4cc78-2a1d-4185-9e9b-18b3b909f674","order_by":0,"name":"Ningning Mei","email":"","orcid":"","institution":"The Second Hospital of Hebei Medical University","correspondingAuthor":false,"prefix":"","firstName":"Ningning","middleName":"","lastName":"Mei","suffix":""},{"id":380979497,"identity":"1faef1f3-9235-4e2f-a0a5-56e4273b9543","order_by":1,"name":"Lei Li","email":"","orcid":"","institution":"The Second Hospital of Hebei Medical University","correspondingAuthor":false,"prefix":"","firstName":"Lei","middleName":"","lastName":"Li","suffix":""},{"id":380979498,"identity":"037f63f3-9903-4fee-8cd9-bf5148bd42ba","order_by":2,"name":"Yan Cui","email":"","orcid":"","institution":"The Second Hospital of Hebei Medical University","correspondingAuthor":false,"prefix":"","firstName":"Yan","middleName":"","lastName":"Cui","suffix":""},{"id":380979499,"identity":"689704b7-1c6d-4230-ab92-f737b1356418","order_by":3,"name":"Liang Wang","email":"","orcid":"","institution":"The Second Hospital of Hebei Medical University","correspondingAuthor":false,"prefix":"","firstName":"Liang","middleName":"","lastName":"Wang","suffix":""},{"id":380979500,"identity":"1827091d-eb73-4b40-83f9-5e98edcd5ec6","order_by":4,"name":"Hong Jiang","email":"","orcid":"","institution":"The Second Hospital of Hebei Medical University","correspondingAuthor":false,"prefix":"","firstName":"Hong","middleName":"","lastName":"Jiang","suffix":""},{"id":380979501,"identity":"f9225be1-4069-47cc-bbfe-1cd96a84ac77","order_by":5,"name":"Xinying Tian","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA70lEQVRIiWNgGAWjYBACfvbmAwcSKv7L8UswsEGEDhDQItlzLPHBhzPMxpIziNVicMPH2HBmG3PihhvEamG4wZYmzXOGzdj4dvOxRzfbGOT4biQwfi7Ao4NxdvMxaZ4KHjmzO8fSjXPbGIwlbyQwS8/Ao4VZ5hjIFgljsxs5ZtJALUAXJrAx8+DRwiYBVMnbZpC4eUb+N5CWeoJaeCRyQN5PSNwgkcMG0pJgQEiLBA84kA8YS9xIMzfOOSdhOPPMw2ZpfFrsj4Oj8oAc/4zkZ49zymzk+Y4nH/yMTwuGrUDM2ECChlEwCkbBKBgF2AAAEKlQ+6Syc4IAAAAASUVORK5CYII=","orcid":"","institution":"The Second Hospital of Hebei Medical University","correspondingAuthor":true,"prefix":"","firstName":"Xinying","middleName":"","lastName":"Tian","suffix":""}],"badges":[],"createdAt":"2024-11-13 14:38:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5447826/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5447826/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":71925711,"identity":"53a965fe-d3d1-4c7d-8423-952693802249","added_by":"auto","created_at":"2024-12-19 18:41:17","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":68194,"visible":true,"origin":"","legend":"\u003cp\u003eA: diffuse brown spots on the backs of both hands; B: yellow-brown patches on the frontal face; C: atrophic thinning of the right toenail.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5447826/v1/b8d3c80e7e001c8b9701e4e3.jpg"},{"id":71925989,"identity":"4e2f05c2-0f82-42f8-805d-0e0d3b50dccb","added_by":"auto","created_at":"2024-12-19 18:49:17","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":86826,"visible":true,"origin":"","legend":"\u003cp\u003epedigree verification by Sanger DNA sequencing\u003c/p\u003e\n\u003cp\u003eA: Heterozygous mutation in exon 1 from cytosine C to thymine T (c.169C\u0026gt;T) at nucleotide 169, variant originated from the father.\u003c/p\u003e\n\u003cp\u003eB: Heterozygous mutation in exon 12 from cytosine C to adenine A (c.1802C\u0026gt;A) at nucleotide 1802 with variant originating from the mother\u003c/p\u003e\n\u003cp\u003eC: heterozygous mutation in exon 9 c.1378+5G\u0026gt;A, father's origin.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5447826/v1/d2ed66e4a09240ca29226e89.jpg"},{"id":71925166,"identity":"142c4fa6-122f-4fb6-b92e-c7dee74b3a5a","added_by":"auto","created_at":"2024-12-19 18:33:17","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":86567,"visible":true,"origin":"","legend":"\u003cp\u003eSLC6A19 3D structural model prediction results\u003c/p\u003e\n\u003cp\u003eA1,B1 are the overall picture, A2,B2 are the local zoomed-in picture, and A3,B3 are the Sticks plot. The left column represents the wild type, while the right column depicts the mutant type.\u003c/p\u003e\n\u003cp\u003eA exon1 c.169C\u0026gt;T mutation, Amino acid Arg(R) at position 57 is mutated to amino acid Cys(C) in the wild-type SLC6A19 protein.\u003c/p\u003e\n\u003cp\u003eB exon12 c.1802C\u0026gt;A mutation, Amino acid Ala at position 601 is mutated to amino acid Asp in the wild-type SLC6A19 protein.\u003c/p\u003e\n\u003cp\u003eIn the cartoon structure in the figure, blue represents α-helix, purple represents β-folding, pink coils represent Loop structure and the figure shows the hydrogen bonding observed as stick structure, where each colour represents a different atom, yellow-C atom, grey-H atom, blue-N atom, red-O atom, orange-S atom, and hydrogen bonding is in green.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5447826/v1/b29e4fca75e4c47a6d01b37d.jpg"},{"id":71925713,"identity":"0c553fa6-c78c-4fd9-b408-becd9253c43e","added_by":"auto","created_at":"2024-12-19 18:41:17","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":88927,"visible":true,"origin":"","legend":"\u003cp\u003eConservation analysis of amino acid sequences\u003c/p\u003e\n\u003cp\u003eMultiple sequence comparisons showed that amino acid 57 of SLC6A19 protein is Arg(R) and that amino acid 601 is Ala(A) both of which are conserved across several mammals including human (shown by red arrow).\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5447826/v1/961f51b025514c7a3c45d481.jpg"},{"id":75119216,"identity":"71ddc09e-2602-4841-b0ca-e9393a0ef895","added_by":"auto","created_at":"2025-01-30 16:53:34","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":747249,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5447826/v1/e3d5e101-ed3e-4325-a006-77967fb3e899.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Hartnup disease combined with iminocaciduria: two novel mutations in the SLC6A19 gene (a case report)","fulltext":[{"header":"Introduction","content":"\u003cp\u003eHartnup disease is a rare autosomal recessive disease discovered in 1956 \u003csup\u003e1\u003c/sup\u003e, characterized by neutral aminoaciduria, pellagra-like skin symptoms (including pigmentation and discoloration in sun-exposed areas), ataxia, and various psychiatric manifestations. The clinical features and course of the disease can be variable. However, aminoaciduria remains a persistent finding \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e.The etiology of the disease is attributed to a mutation in the SLC6A19 gene, which encodes the neutral amino acid transport protein. The incidence rate in the European population is approximately 1 in 30,000. This report presents a case of Hartnup disease combined with iminocaciduria, outlining clinical manifestations and pedigree analysis, with the aim of enhancing awareness of this condition.\u003c/p\u003e"},{"header":"Case presentation","content":"\u003cp\u003eThe patient is a 34-year-old unmarried male who was admitted due to unsteady walking persisting for one year. The instability arose unexpectedly, characterized by a leftward tilt, intermittent limb tremors, and multiple falls. The patient demonstrated significant upper limb strength but no limb numbness or sensory abnormalities in his extremities. Medical history reveals that 23 years prior, the patient began to exhibit withdrawn and passive behavior, avoiding social interactions with peers and showing a lack of response to those around him. He spoke softly and often lowered his head. Eleven years ago, upon entering the workforce, he developed heightened sensitivity and suspicion, remaining perpetually on edge and frequently glancing around anxiously. A year ago, due to his pronounced sensitivity and behavioral abnormalities, he was diagnosed with schizophrenia at another hospital. Additionally, the patient experiences \u0026ldquo;photosensitivity,\u0026rdquo; evident by rough, pigmented skin on sun-exposed areas such as the hands and face during the summer months, with improvement noted by the season's end. There is no reported history of birth injuries or asphyxia, and there is no similar family history; his parents are not closely related. Upon physical examination at the time of admission: diffuse brown spots with slightly rough surfaces and a few fine, fragmented scales were observed on the backs of both hands (Fig.\u0026nbsp;1A). Brownish-yellow patches with well-defined borders are noted on the forehead and face (Fig.\u0026nbsp;1B). The right toenail exhibited atrophy and thinning, accompanied by a rough surface (Fig.\u0026nbsp;1C).\u003c/p\u003e \u003cp\u003eNeurological examination revealed that the patient was alert and articulates clearly, albeit demonstrating sluggish reactions without significant memory deficits. Small, intermittent horizontal nystagmus was noted. Muscle strength assessment showed 4\u0026thinsp;+\u0026thinsp;in the proximal lower limbs and 5 in the distal lower limbs. Increased muscle tone was observed in the right lower limb, presenting a \u0026ldquo;knife-like\u0026rdquo; appearance. Upper limb tendon reflexeswere intact, while lower limb tendon reflexes were markedly exaggerated (+++++). Both Babinski's signs were positive. No notable abnormalities were detected during the sensory system evaluation. In the coordination assessment, the right-sided finger-to-nose test was unstable and inaccurate. No neck stiffness was noted. There was no significant delay in bilateral finger-to-finger or fist clenching. No tremors or involuntary movements were observed. Gait analysis reveaed an abnormal pattern characterized by a wide base, threshold-crossing gait, and impaired tandem gait.\u003c/p\u003e \u003cp\u003eLaboratory tests, including routine assessments of blood, urine, and stool tests, as well as evaluations of myocardial enzymes, electrolytes, liver and kidney function, thyroid function, and D-dimer levels, revealed no significant abnormalities. Cerebrospinal fluid (CSF) analyses, encompassing both routine and biochemical tests, were within normal limits. Additionally, tests for autoantibodies, autoimmune encephalitis antibodies in both blood and CSF, and paraneoplastic antibodies returned negative results. An abdominal ultrasound yielded unremarkable findings.\u003c/p\u003e \u003cp\u003eCranial imaging: Diffusion-weighted imaging (DWI) and MRI of the brain revealed scattered ischemic lesions in the bilateral frontal lobes, right parietal lobe, and corona radiata, and the left insular lobe. No discernible diffusion-restricted signals were identified within the brain parenchyma.\u003c/p\u003e \u003cp\u003eElectromyography (EMG) revealed damage to the motor fibers of the bilateral common peroneal nerves and tibial nerves, with \"F\" waves failing to elicite from the bilateral common peroneal nerves. A video electroencephalogram (EEG) demonstrated widespread θ theta slow wave activity. Cognitive screening yielded a Mini-Mental State Examination (MMSE) score of 26 and a Montreal Cognitive Assessment (MoCA) score of 24. Urinary organic acid analysis showed elevated levels of 5-oxoproline and proline. Blood tests for genetic metabolic disorders, including amino acid and acylcarnitine profiles, did not reveal any abnormalities in neutral amino acids.\u003c/p\u003e \u003cp\u003eGenetic testing: With the patient's informed consent, whole exome sequencing was performed using venous blood samples (conducted by MyGenostics, Beijing). The results revealed three heterozygous mutations in the SLC6A19 gene: 1. Exon 1: A heterozygous mutation at nucleotide 169, where cytosine (C) is replaced by thymine (T) (c.169C\u0026thinsp;\u0026gt;\u0026thinsp;T), results in a missense mutation that changes the amino acid from arginine to cysteine at position 57 (p.R57C) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003eA);2. Exon 12: A heterozygous mutation at nucleotide 1802, where cytosine (C) is replaced by adenine (A) (c.1802C\u0026thinsp;\u0026gt;\u0026thinsp;A), causes another missense mutation that changes the amino acid from alanine to aspartic acid at position 601 (p.A601D) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003eB). 3. Exon 9: A heterozygous mutation at c.1378\u0026thinsp;+\u0026thinsp;5G\u0026thinsp;\u0026gt;\u0026thinsp;A, leading to a splicing mutation (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003eC). Pedigree verification by Sanger DNA sequencing revealed that the c.169C\u0026thinsp;\u0026gt;\u0026thinsp;T and c.1378\u0026thinsp;+\u0026thinsp;5G\u0026thinsp;\u0026gt;\u0026thinsp;A mutations were inherited from the father, while the c.1802C\u0026thinsp;\u0026gt;\u0026thinsp;A mutation was inherited from the mother. The family pedigree is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eProtein model building and functional prediction: The wild-type 3D model of the SNCA gene was retrieved from the SWISS-MODEL database (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://swissmodel.expasy.org/\u003c/span\u003e\u003cspan address=\"https://swissmodel.expasy.org/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e), identified as Q9D687.1.A and encompassing residues 1-633. This model displays a sequence similarity of 58% and a sequence identity of 86.89% indicating a high degree of relatedness to the template structure. The modeling quality, assessed by the GMQE score is 0.9, which suggests excellent model quality and strong consistency with experimentally determined structures. The homologous model data were visualized using PyMOL (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://pymol.org/2/\u003c/span\u003e\u003cspan address=\"https://pymol.org/2/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e)\u003csup\u003e3\u0026ndash;6\u003c/sup\u003e .Functional predictions were conducted for the mutations c.169C\u0026thinsp;\u0026gt;\u0026thinsp;T and c.1802C\u0026thinsp;\u0026gt;\u0026thinsp;A, aimed at assessing their potential impact on protein function and stability, the results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eFor the SLC6A19 mutation NM_001003841 c.169C\u0026thinsp;\u0026gt;\u0026thinsp;T (p.R57C), the wild-type SLC6A19 protein features arginine (Arg, R) at position 57, which is replaced by cysteine (Cys, C) due to this mutation. After this mutation, the number and length of hydrogen bonds remain unchanged. Here are the potential effects of this substitution on the protein: 1.Charge Change: Arginine has a positive charge, while cysteine has a neutral thiol group. This change can significantly alter the protein\u0026rsquo;s charge distribution, potentially affecting its interactions with other molecules. 2. Polarity Change: Cysteine has weaker polarity compared to arginine, which might impact the protein's solubility and stability (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). For the SLC6A19 mutation NM_001003841 c.1802C\u0026thinsp;\u0026gt;\u0026thinsp;A (p.A601D) mutation, the wild-type SLC6A19 protein features alanine (Ala, A) at position 601, which is replaced by aspartic acid (Asp, D) due to this mutation. The number and length of hydrogen bonds remain unchanged after the mutation. Here are the potential effects of this substitution on the protein: 1. Charge Change: Alanine is neutral, while aspartic acid carries a negative charge. This substitution may alter the protein's charge distribution, potentially affecting its interactions with other molecules. 2. Polarity Change: Alanine is non-polar, whereas aspartic acid is polar. The introduction of a polar side chain in place of a non-polar side chain may influence the protein's solubility, stability, and overall conformation. 3. Conformational Flexibility: Alanine's short, non-polar side chain usually generally contributes to greater flexibility in the protein structure, while aspartic acid's polar side chain may restrict this flexibility, affect the protein's dynamics and conformational changes necessary for its function (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003eB).\u003c/p\u003e \u003cp\u003eBioinformatics Analysis: By comparing the differences in amino acid sequences of the mutations with those of other animals using database resources, multiplex sequence alignment results showed that the SLC6A19 protein had an Arg(R) at amino acids 57 and Ala(A) at amino acids 601, which are conserved across multiple mammals, including humans (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003e, indicated by red arrows). Specifically, position 57 is arginine (Arg, R) and position 601 is alanine (Ala, A).Using comprehensive bioinformatics protein function prediction tools such as REVEL, SIFT, PolyPhen_2, MutationTaster, and GERP, the predictions for the c.169C\u0026thinsp;\u0026gt;\u0026thinsp;T (p.R57C) and c.1802C\u0026thinsp;\u0026gt;\u0026thinsp;A (p.A601D) mutations indicate that both mutations are likely harmful. This suggests that they may disrupt the normal function of the SLC6A19 protein, potentially contributing to pathologies associated with its dysfunction, such as Hartnup disorder or other related conditions. A heterozygous mutation at c.1378\u0026thinsp;+\u0026thinsp;5G\u0026thinsp;\u0026gt;\u0026thinsp;A, leading to a splicing mutation, may affect the normal splicing of the pre-mRNA, potentially resulting in an incorrect or truncated protein product.\u003c/p\u003e \u003cp\u003eTreatment: The patient received intravenous niacin treatment followed by a prescription for oral extended-release niacin tablets (0.5 g) to be taken once daily at night after discharge. The patient's rash improved, and his mental state and mood restored to a normal level. This indicates a positive response to niacin treatment.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe classic clinical manifestations of Hartnup disease include intermittent pellagra-like dermatitis (rashes), cerebellar ataxia, and psychiatric symptoms\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. In this case, the patient exhibited withdrawn and passive behavior from an early age, and gradually developed psychiatric symptoms including heightened sensitivity and anxiety. He was hospitalized for schizophrenia and exhibited mild cognitive impairment, along with progressive symptoms such as unsteady walking, tremors, frequent falls, and impaired coordination. Photosensitive pellagra-like changes were observed on the skin of the patient's hands and face, which are consistent with the clinical features of Hartnup disease. Using high-throughput and Sanger sequencing, three mutation sites in the SLC6A19 gene were identified: two heterozygous missense mutations of c.1802C\u0026thinsp;\u0026gt;\u0026thinsp;A and c.169C\u0026thinsp;\u0026gt;\u0026thinsp;T, and a heterozygous splicing mutation of c.1378\u0026thinsp;+\u0026thinsp;5G\u0026thinsp;\u0026gt;\u0026thinsp;A. The patient, possessing compound heterozygous mutations, was ultimately diagnosed with Hartnup disease.\u003c/p\u003e \u003cp\u003eIn 2004, the causative gene for Hartnup disease was cloned and identified as the SLC6A19 gene located on chromosome 5p15\u003csup\u003e8\u003c/sup\u003e. This gene encodes a sodium- and chloride-dependent neutral amino acid transporter B0AT1, which is primarily expressed in the kidney and small intestine. B0AT1 serves as a critical transporter responsible for over 95% of the absorption of free neutral amino acids in the small intestine and their subsequent reabsorption in the kidney\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. The metabolic defect in Hartnup disease arises from the dysfunction of the neutral amino acid transporter, resulting in excessive loss of various amino acids in urine. A key issue is the impaired transport of tryptophan, which disrupts the disruption of the tryptophan-kynurenine-niacinamide metabolic pathway. This impairment results in reduced tryptophan absorption and increased production of indole, inhibiting niacin synthesis and causing niacin deficiency. Niacin deficiency can manifest as pellagra-like skin rashes and neurological damage. Pellagra-like rashes may either spontaneously resolve or improve following niacin treatment and typically present as photosensitive dermatitis\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. Neurological symptoms associated with Hartnup disease encompass episodic ataxia, behavioral disturbances, and psychiatric issues such as anxiety, depression, and mild intellectual disability\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. Additional potential symptoms include tremors, seizures\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e, diplopia, spastic paraplegia, and peripheral neuropathy\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e.A case reported by Jiang Wei et al.\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003eshowed that the levels of neutral amino acids in the urine of a proband were significantly elevated above standard values, indicating that mutations in the SLC6A19 gene lead to neutral amino acid transport disorders and hyperaminoaciduria. A limitation of this case is the absence of urinary neutral amino acid levels testing for the patient, and future assessments could further validate the metabolic alterations associated with this condition. The father of the patient in this case has two mutation sites, namely c.169C\u0026thinsp;\u0026gt;\u0026thinsp;T (p.Ary57Cys) and c.1378\u0026thinsp;+\u0026thinsp;5G\u0026thinsp;\u0026gt;\u0026thinsp;A. The mutation c.169C\u0026thinsp;\u0026gt;\u0026thinsp;T has been reported as a pathogenic mutation\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. However, there are no relevant reports in the literature database regarding c.1802C\u0026thinsp;\u0026gt;\u0026thinsp;A and c.1378\u0026thinsp;+\u0026thinsp;5G\u0026thinsp;\u0026gt;\u0026thinsp;A, suggesting that these are novel mutations.\u003c/p\u003e \u003cp\u003eThe SLC6A19 gene comprises 12 exons, and it has been reported that specific mutations in exons 1, 6, and 12 may severely impair the function of the B0AT1 transporter, leading to noticeable clinical manifestations of Hartnup disease. Conversely, other mutations may cause aminoaciduria without presenting any symptoms\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. Mutations located within the transmembrane domains of the SLC6A19 transporter can result in dysfunction of the protein, leading to pronounced neutral aminoaciduria, skin issues, and neurological symptoms. In contrast, mutations outside of the transmembrane domains, however, may only partially affect the transporter's function\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e, resulting in milder clinical manifestations. According to the topological model of human SLC6A19 described by Br\u0026ouml;er S\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e, the mutations c.169C\u0026thinsp;\u0026gt;\u0026thinsp;T (p.Arg57Cys) and c.1802C\u0026thinsp;\u0026gt;\u0026thinsp;A (p.A601D) are located in the transmembrane regions of exons 1 and 12, respectively. Therefore, these mutations are likely to cause transporter dysfunction and lead to clinical symptoms. Additionally, our protein modeling and prediction results indicate that the mutations at these two sites are pathogenic, further reinforcing this conclusion. However, experimental studies may be required to characterize these changes fully and understand their biological significance, especially in the context of disorders associated with SLC6A19 dysfunction. The SLC6A19 gene plays a crucial role in the renal reabsorption of neutral amino acids.\u003c/p\u003e \u003cp\u003eMutations in SLC6A19 can also affect the transport of imino acids and glycine in the kidneys and intestines. This dysfunction may lead to conditions such as iminoglycinuria (IG) and hyperglycinuria (HG)\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. In the kidneys, the transport of proline and glycine is mediated by four transport proteins: SLC36A2 (PAT2): Proline and glycine transporter, SLC6A18 (B0AT3 or XT2): Glycine transporter,SLC6A19 (B0AT1): Neutral amino acid transporter, SLC6A20 (IMINO or SIT1): Proline-specific transporter\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e.The main genes associated with iminoglycinuria and hyperglycinuria are SLC36A2 and SLC6A20. Genetic variations in SLC6A18 or SLC6A19 alone are generally insufficient to cause iminoglycinuria or hyperglycinuria \u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. In humans, the kidneys exhibit a stronger capacity for proline reabsorption compared to glycine, with most proline reabsorption being mediated by SLC36A2.\u003c/p\u003e \u003cp\u003eIminoglycinuria is inherited in an autosomal recessive manner and is characterized by increased excretion of proline and glycine in the urine. Both Iminoglycinuria and hyperglycinuria can present with a range of symptoms including hypertension, diabetes, kidney stones, intellectual disability, atypical chorioretinal atrophy, hearing loss, and blindness\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e.Hyperglycinuria is generally the result of defects in glycine metabolism or abnormalities in the renal tubular reabsorption of glycine. Excessive glycine levels can lead to elevated oxalate levels, as glycine is involved in the metabolic pathways that generate oxalate. Defects in oxalate transport can result in increased urinary oxalate content which may cause damage to renal tubular epithelial cells. This damage can promote the formation of calcium oxalate stones. Pan et al.\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003ereported a case of a young male patient from China with hyperglycinuria attributed to the SLC6A19 c.1278C\u0026thinsp;\u0026gt;\u0026thinsp;T (p.Cys426) mutation, this patient ultimately exhibited bilateral calcium oxalate kidney stones.\u003c/p\u003e \u003cp\u003eMutations in the SLC6A19 gene can lead to impaired renal reabsorption of amino acids and disrupt the transport of related metabolites. Although SLC6A19 is also involved in the transport of proline and glycine, Hartnup disease is characterized by the excretion of all neutral amino acids, except for proline, in the urine\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. In this case, the patient exhibited typical symptoms of Hartnup disease, with elevated levels of 5-hydroxyproline in the urine. Although urinary glycine levels were not tested, the absence of kidney stones indicates that glycine transport function may not be significantly affected, distinguishing this case from generalized hyperglycinuria. Therefore, Hartnup disease with iminoglycinuria is considered. Iminoglycinuria refers to the excretion of imino acids, primarily proline and hydroxyproline, along with some neutral amino acids, which results from the impaired reabsorption mechanisms.\u003c/p\u003e \u003cp\u003eIn summary, Hartnup disease is a rare, treatable genetic metabolic disease characterized by intermittent pellagra-like dermatitis (rashes), cerebellar ataxia, psychiatric symptoms, and neutral aminoaciduria. Genetic testing is crucial for diagnosis. In this case, two novel mutation sites, c.1802C\u0026thinsp;\u0026gt;\u0026thinsp;A and c.1378\u0026thinsp;+\u0026thinsp;5G\u0026thinsp;\u0026gt;\u0026thinsp;A, were identified, thereby expanding the genetic spectrum associated with Hartnup disease. The diagnosis of Hartnup disease combined with iminoglycinuria provides a comprehensive understanding of the patient's condition.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCSF\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eCerebrospinal fluid\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eDWI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eDiffusion-weighted imaging\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMRI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eMagnetic resonance imaging\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eEMG\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eElectromyography\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eEEG\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eelectroencephalogram\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMMSE\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eMini-Mental State Examination\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMoCA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eMontreal Cognitive Assessment\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eIG\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eiminoglycinuria\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eHG\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ehyperglycinuria.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWritten informed consent was obtained from the patient for publication of this case report and any accompanying images.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the data analysed during this study are included in this article.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNone.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to thank the patient for their cooperation, their patience in providing the necessary information.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u003c/strong\u003e\u003cstrong\u003e’\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003econtributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNingning Mei: case report concept and design, data collection, drafting of the manuscript;\u003c/p\u003e\n\u003cp\u003eLei Li, Yan Cui, Liang Wang, Hong Jiang: patient’s clinical and paraclinical management;\u003c/p\u003e\n\u003cp\u003eXinying Tian: provided supervision and revised the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBARON DN, DENT CE, HART HARRISH, JEPSON EW. Hereditary pellagra-like skin rash with temporary cerebellar ataxia, constant renal amino-aciduria, and other bizarre biochemical features. Lancet. 1956;271(6940):421\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBr\u0026ouml;er A, Juelich T, Vanslambrouck JM, et al. Impaired nutrient signaling and body weight control in a Na\u0026thinsp;+\u0026thinsp;neutral amino acid cotransporter (Slc6a19)-deficient mouse. J Biol Chem. 2011;286(30):26638\u0026ndash;51.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBiasini M, Bienert S, Waterhouse A et al. SWISS-MODEL: modelling protein tertiary and quaternary structure using evolutionary information. Nucleic Acids Res. 2014. 42(Web Server issue): W252\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKiefer F, Arnold K, K\u0026uuml;nzli M, Bordoli L, Schwede T. The SWISS-MODEL Repository and associated resources. Nucleic Acids Res. 2009;37(Database issue):D387\u0026ndash;92.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eArnold K, Bordoli L, Kopp J, Schwede T. The SWISS-MODEL workspace: a web-based environment for protein structure homology modelling. Bioinformatics. 2006;22(2):195\u0026ndash;201.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuex N, Peitsch MC, Schwede T. Automated comparative protein structure modeling with SWISS-MODEL and Swiss-PdbViewer: a historical perspective. Electrophoresis. 2009;30(Suppl 1):S162\u0026ndash;73.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang X, Li XY, Piao Y, et al. Hartnup disease presenting as hereditary spastic paraplegia and severe peripheral neuropathy. Am J Med Genet A. 2022;188(1):237\u0026ndash;42.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKleta R, Romeo E, Ristic Z, et al. Mutations in SLC6A19, encoding B0AT1, cause Hartnup disorder. Nat Genet. 2004;36(9):999\u0026ndash;1002.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBelanger AJ, Gefteas E, Przybylska M, et al. Excretion of excess nitrogen and increased survival by loss of SLC6A19 in a mouse model of ornithine transcarbamylase deficiency. J Inherit Metab Dis. 2023;46(1):55\u0026ndash;65.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZheng Y, Zhou C, Huang Y, Bu D, Zhu X, Jiang W. A novel missense mutation in the SLC6A19 gene in a Chinese family with Hartnup disorder. Int J Dermatol. 2009;48(4):388\u0026ndash;92.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCheon CK, Lee BH, Ko JM, Kim HJ, Yoo HW. Novel mutation in SLC6A19 causing late-onset seizures in Hartnup disorder. Pediatr Neurol. 2010;42(5):369\u0026ndash;71.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWei Jiang S, Li C, Zhou Y, Huang, Dingfang PU, Xunjun, Zhu. Analysisofm utatiosin the SLC6A 19 gene in a Chinese family witIlH artnup disease. China J Lepr Skin Dis. 2009;25(12):877\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNozaki J, Dakeishi M, Ohura T, et al. Homozygosity mapping to chromosome 5p15 of a gene responsible for Hartnup disorder. Biochem Biophys Res Commun. 2001;284(2):255\u0026ndash;60.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhu Y, Chen L, He J, et al. Study of Seizure-Manifested Hartnup Disorder Case Induced By Novel Mutations in SLC6A19. Open Life Sci. 2018;13:22\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBr\u0026ouml;er S. The role of the neutral amino acid transporter B0AT1 (SLC6A19) in Hartnup disorder and protein nutrition. IUBMB Life. 2009;61(6):591\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBr\u0026ouml;er S, Bailey CG, Kowalczuk S, et al. Iminoglycinuria and hyperglycinuria are discrete human phenotypes resulting from complex mutations in proline and glycine transporters. J Clin Invest. 2008;118(12):3881\u0026ndash;92.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVanslambrouck JM, Br\u0026ouml;er A, Thavyogarajah T, et al. Renal imino acid and glycine transport system ontogeny and involvement in developmental iminoglycinuria. Biochem J. 2010;428(3):397\u0026ndash;407.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKukułowicz J, Pietrzak-Lichwa K, Klimończyk K, Idlin N, Bajda M. The SLC6A15-SLC6A20 Neutral Amino Acid Transporter Subfamily: Functions, Diseases, and Their Therapeutic Relevance. Pharmacol Rev. 2023;76(1):142\u0026ndash;93.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBr\u0026ouml;er A, Cavanaugh JA, Rasko JE, Br\u0026ouml;er S. The molecular basis of neutral aminoacidurias. Pflugers Arch. 2006;451(4):511\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePan Y, Wang S, Liu L, Liu X. The SLC6A19 gene mutation in a young man with hyperglycinuria and nephrolithiasis: a case report and literature review. BMC Urol. 2022;22(1):190.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Hartnup disease, SLC6A19 gene, Novel mutations, iminocaciduria","lastPublishedDoi":"10.21203/rs.3.rs-5447826/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5447826/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003ePurpose\u003c/h2\u003e \u003cp\u003eTo report a case of Hartnup disease combined with iminocaciduria, and to explore its clinical manifestations and genetic mutations.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eClinical data of the patient were collected, whole-exome sequencing was performed using high-throughput sequencing technology to detect SLC6A19 gene mutations. Sanger sequencing was used for family verification, and software was employed to predict protein structure and function.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eThe patient exhibited intermittent pellagra, ataxia, and psychiatric symptoms. Genetic sequencing revealed three heterozygous mutations in the SLC6A19 gene: a heterozygous missense mutation c.169C\u0026thinsp;\u0026gt;\u0026thinsp;T (p.Ary57Cys), a heterozygous missense mutation c.1802C\u0026thinsp;\u0026gt;\u0026thinsp;A (p.A601D), and a heterozygous splicing mutation c.1378\u0026thinsp;+\u0026thinsp;5G\u0026thinsp;\u0026gt;\u0026thinsp;A. The c.169C\u0026thinsp;\u0026gt;\u0026thinsp;T and c.1378\u0026thinsp;+\u0026thinsp;5G\u0026thinsp;\u0026gt;\u0026thinsp;A mutations were inherited from the father, whereas the mutation c.1802C\u0026thinsp;\u0026gt;\u0026thinsp;A was passed down from the mother. Bioinformatics-based protein function prediction indicated that both the c.169C\u0026thinsp;\u0026gt;\u0026thinsp;T (p.R57C) and c.1802C\u0026thinsp;\u0026gt;\u0026thinsp;A (p.A601D) mutations are harmful. Furthermore, the levels of 5-oxoproline and proline in the urine were elevated.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eThe typical manifestations of Hartnup disease include intermittent pellagra, ataxia, and psychiatric symptoms. The SLC6A19 mutations c.1802C\u0026thinsp;\u0026gt;\u0026thinsp;A and c.1378\u0026thinsp;+\u0026thinsp;5G\u0026thinsp;\u0026gt;\u0026thinsp;A are novel, and this case expands the genetic spectrum of the disease.\u003c/p\u003e","manuscriptTitle":"Hartnup disease combined with iminocaciduria: two novel mutations in the SLC6A19 gene (a case report)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-19 18:33:12","doi":"10.21203/rs.3.rs-5447826/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"61459fac-1901-4965-bea3-60d3e063e60a","owner":[],"postedDate":"December 19th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-02-17T04:53:10+00:00","versionOfRecord":[],"versionCreatedAt":"2024-12-19 18:33:12","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5447826","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5447826","identity":"rs-5447826","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}