Rare duplication of the CDC73 gene and atypical hyperparathyroidism-jaw tumor syndrome: A case report and review of the literature

As part of a routine workup of unexplained weight gain in a 28‐year‐old Caucasian woman, a pHPT was diagnosed with a calcemia at 2.67 mmol/L (normal 2.12–2.52 mmol/L), a phosphatemia at 0.8 mmol/L (normal 0.81–1.58 mmol/L), a parathormone (PTH) concentration of 66.2 ng/L (18.4–80.1 ng/L), and a 24‐h calciuria level of 8.58 mmol/24 h (normal 1–8.80 mmol/24 h). An ultrasound performed found in the posteroinferior part of the right lobe a small hypoechoic pseudo‐nodular structure with a regular contour measuring 9 mm which could correspond to a parathyroid hypertrophy. Choline PET/CT found a hyperfixation more focused posteroinferior right thyroid, well separated from the thyroid lobe, which may correspond to a parathyroid adenoma P3 right (SU VMAX = 3.62) ( Figure  1 ) . [ 99m Tc]TC‐MIBI scintigraphy Methoxy‐isobutyl‐isonitrile scintigraphy appeared negative. Waiting for genetics results, a screening of MEN1‐associated lesions was performed. Pituitary MRI found about a right lateralized hypoenhancement without abnormality in the other sequences measuring 5 × 4 mm that requires new look. A thoracic‐abdominal‐pelvic CT scan (TAP‐CT) found a pancreatic mass at 7 mm, not confirmed using echo‐endoscopy. Plasma chromogranin A, gastrin, and pancreatic polypeptide were within normal limits, as were pituitary bioassays. Renal ultrasound was normal, while bone densitometry showed osteopenia with a femoral T‐score of −2.4. Choline PET/CT of proband. PET VCAR found a hyperfixation of posteroinferior right thyroid, well separated from the thyroid lobe, which may correspond to a parathyroid adenoma P3 right (SU VMAX = 3.62). The arrow indicates the right parathyroid lesion in PET/CT (1) and CT (2). Her family history is marked by the occurrence of a pHPT in her mother, discovered at 50 years old, induced by a parathyroid adenoma operated at 52 years old, discovered incidentally during a routine blood test. This patient had a total hysterectomy at the age of 48 years for menometrorrhagia, present since one year and unresolved by progestin and levonorgestrel treatment. Anatomopathology concluded to a moderate uterine parietal adenomyosis with no sign of malignancy. Due to the young age of the index case (<50 years old) and family history (two first degree relatives is an indication for analysis Figure  2 ), a first‐line panel by NGS of the genes involved in pHPT was undertaken (Table  1 ). A heterozygous pathogenic variation in the CDC73 gene was found: c.687_688dup, p.Val230Glufs*28 (or previously reported as c.679_680insAG; p.Arg227fs*31) which inserts two nucleotides in exon 7 causing a frameshift at codon 230, this creates a stop gain and a loss of function of the allele (Figure  3 ). This variation was confirmed by Sanger method on a second independent sample. The familial genetic investigation found the variant in her mother. The at risk relatives in this branch refused the genetic analysis. Following the discovery of this variation, an extension workup was undertaken in the two patients, associating a dental panoramic, a renal and pelvic ultrasound to look for tumors of the jaw, uterine lesions, or renal abnormalities, respectively, found no anomalies. Preoperative neck ultrasound do not show features suggestive of parathyroid carcinoma such as infiltration, calcification, irregular borders, or signs of local invasion. Therefore, mini‐invasive surgery of right P3 parathyroid gland was performed. Histological examination found no malignancy criteria. Calcemia was normalized after surgery. Follow‐up two years after diagnosis did not found any new lesions in these patients. Family tree. Apart from the index case and his mother, there is no other history of hyperparathyroidism or symptoms of the HPT‐JT spectrum. The arrow indicates the proband. Panel of genes involved in hyperparathyroidism analyzed Note : These genes are part of our first‐line panel because they are the most frequently involved in familial primary hyperparathyroidism. CDC73 gene germline variation. *A germline mutation was identified in CDC73 gene, which changed codon 230 in exon 7 from valine to glutamine and leads to a frameshift with the appearance of a stop codon. The identification of this mutation is in favor of a HPT‐JT.

MC, and GG designed the study; GG, MBL, AK, MC and FP‐C, performed the acquisition of data; GG, MBL, NU, MP, FP‐C, AK, MGB, SV, YB, YJB and MC performed analysis, interpretation of data, and critically revised the article; GG, MBL and MC drafted the article.

The study has been approved by personal protection committee (IRB: 2021/CE 57).

Centre Jean Perrin.

Patients consented to research.

A first‐line panel of four genes containing CaSR ( NM_000388.3 ), CDC73 ( NM_024529.4 ), MEN1 ( NM_130799.2 ), and RET ( NM_020975.4 ). Samples underwent a fragmentation, capture, and sequencing protocol. Data for unrequested genes were marked before bio‐informatic processing and interpretation. Sonic fragmentation of DNA from peripheral blood was performed on a Bioruptor instrument (Diagenode). Kapa HTP library preparation and SeqCap EZ Choice probes and reagents (Roche) were used for library preparation and capture. Quality of fragmentation, library, and capture were controlled using a Bioanalyzer 2100 instrument (Agilent). Sequencing was performed using Miseq v2 kit (300 cycles) on MiSeq Instrument (Illumina). All steps were performed following providers' guidelines. All class 5 (pathogenic) or 4 (likely pathogenic) variants were confirmed on a second patient sample. De‐multiplexing was performed using bcl2fastq2 Conversion Software (Illumina). Alignment was performed on University of California Santa Cruz human genome reference build 19 using the Burrows–Wheeler Aligner. Picard was used to identify duplicate reads and Genome Analysis Toolkit (GATK) for base quality score recalibration (BaseRecalibrator and ApplyBQSR), as recommended by Eurogentest guidelines (Matthijs et al.,  2016 ) and GATK best practices data pre‐processing workflow. Variant calling was performed using GATK HaplotypeCaller and annotated using Ensembl Variant Effect Predictor, ANOVAR, and Splicing Prediction Pipeline (SPiP). A minimum depth of 30X was required and variants were filtered according to “Hard‐filtering germline short variants” recommendations from GATK (Quality by Depth 60, MappingQuality <40, MappingQualityRankSum <−12,5). Variant/CNV interpretation was performed using ALAMUT (Interactive Bio‐Software), which includes splice site analysis tools (SpliceSiteFinder, MaxEntScan), protein‐function prediction tools (SIFT, Polyphen 2.0), and links to relevant databases (ClinVar, Leiden Open Variation Database [LOVD], other syndrome‐specific databases). Variants/CNV were classified according to the American College of Medical Genetics (ACMG) recommendations (Richards et al.,  2015 ).

Approximately 5–10% of pHPT cases are associated with inherited syndromes (Arnold & Marx,  2013 ; Bilezikian et al.,  2018 ; Carpten et al.,  2002 ; Iacobone et al.,  2015 ; Marx et al.,  2002 ; Rosen et al.,  2018 ; Salcuni et al.,  2018 ; Simonds,  2017 ; Thakker,  2016 ). Due to the maternal history of hyperparathyroidism and the young age of the index case, the diagnosis was oriented to a familial syndrome. These syndromes present a high clinical and molecular heterogeneity (Table  2 ) and several diagnoses could be evoked in our index case. The first syndrome to consider in a patient under 30 years of age with pHPT is MEN1. The diagnosis of MEN4 may also be considered despite its rarity (3% of patients with a MEN1 phenotype (Thakker,  2014 )). FHIP or HPT‐JT should also be considered in isolated pHPT. In HPT‐JT, and despite the name of the syndrome, only one third of the patients have jaw involvement (Torresan & Iacobone,  2019 ), whereas almost 100% have pHPT (Iacobone et al.,  2015 ), so the diagnosis can be made in the absence of associated disorders. MEN2 rarely presents with isolated hyperparathyroidism (4–8% of cases (Iacobone et al.,  2015 )) but the diagnosis cannot be ruled out. The absence of hypocalciuria and the presence of osteopenia make the diagnosis of FHH unlikely. Because of this clinical and molecular heterogeneity, the diagnostic strategy currently recommended by the Association of Molecular Genetic Practitioners (ANPGM) is NGS using targeted panels in any patient presenting with a pHPT <50 years old, syndromic or not, with or without family history. The results of the genetic analysis showed a variation in the CDC73 gene associated with HPT‐JT or FHIP. These two entities could be grouped into CDC73 ‐related familial hyperparathyroidism with the same screening and follow‐up program as in HPT‐JT (Newey et al.,  2010 ; van der Tuin et al.,  2017 ). A segregation study was performed and found the variation in the patient's mother. Genes and their association in genetic hyperparathyroidism Note : It is observed that some genes are associated with several different syndromes reflecting clinical and molecular heterogeneity of the hereditary pHPT. In HPT‐JT syndrome, pHPT is present in almost 100% of cases (Iacobone et al.,  2015 ). The main risk of HPT‐JT syndrome is the occurrence of parathyroid carcinoma (PC) which has a high risk of recurrence of about 50% with an overall 10‐year survival of 60–70% (Rodrigo et al.,  2020 ), and is much more frequent in patients with HPT‐JT syndrome, about 23% (Torresan & Iacobone,  2019 ), than in all other cases of pHPT (less than 1% (Walker & Silverberg,  2018 )). At variance with other forms of hereditary pHPT, in HPT‐JT, a single‐gland parathyroid involvement has been reported more frequently (86.1%). multiglandular involvement occurs rarely at initial surgery (13.9% of cases); recurrences of pHPT may occur metachronously in 20% of cases. However, most often patients with the syndrome have a benign parathyroid adenoma (Torresan & Iacobone,  2019 ). Typically, tumors of the jaw, such as ossifying fibroids of the mandible and/or maxilla (Iacobone et al.,  2015 ), are found in 30% of individuals (Torresan & Iacobone,  2019 ), mostly adolescents (Hobbs et al.,  1999 ). Ossifying fibroids of the jaw are benign lesions with less than <0.5% risk of malignant degeneration (Liu et al.,  2010 ). They are histologically different from osteoclastic brown tumors of the pHPT and do not regress after curative parathyroid surgery (Cavaco et al.,  2001 ; Jackson et al.,  1990 ). Although HPT‐JT syndrome is associated with a jaw tumor, it is not the most frequently observed manifestation. Uterine lesions such as adenomyosis, adenofibromas, leiomyomas, endometrial hyperplasia, adenosarcomas, or tumors arising from the Müllerian duct system, are the most frequent symptom after pHPT and are found in 50% of women with HPT‐JT syndrome (Iacobone et al.,  2015 ). A high frequency of menorrhagia requiring hysterectomy has been described in the literature at a mean age of 35 years (range 23–55 years) (Bradley et al.,  2005 ). Decreased reproductive capacity is observed in women with HPT‐JT syndrome with an increased number of miscarriages (Woodard et al.,  2005 ). Fifteen percent of patients with HPT‐JT (Torresan & Iacobone,  2019 ) develop renal lesions, with cystic kidney disease being the most common manifestation. In addition, some patients develop hamartomas and rare renal tumors. Wilms' tumors (Torresan & Iacobone,  2019 ) have been described in three individuals in the literature, which represents <3% of carriers of the CDC73 variation while the incidence in the general population is 1 per 10,000 (Scott et al.,  2006 ). Wilms' tumors normally occur before the age of 5 years (Hobbs et al.,  1999 ), but one case has been reported at the age of 60 years in a HPT‐JT patient (Kakinuma et al.,  1994 ). The index case has an isolated pHPT. His mother had adenomyosis which can be found in HPT‐JT. There is no jaw or renal involvement. Both patients have a discordant atypical phenotype within the same family. HPT‐JT is an extremely rare disease described in the literature in just over 150 families (Torresan & Iacobone,  2019 ) with an incomplete penetrance of 80–95% (Iacobone et al.,  2015 ). Germline variation in the CDC73 gene is found in about 55% of cases in patients with HPT‐JT and in the remaining cases in other conditions such as sporadic parathyroid carcinoma, etc. More than 100 germline or somatic variations of CDC73 have been described. Exon 1 (34%), exon 7 (21%), and exon 2 (17%) are the most frequently involved in germline variations of CDC73 and no variations have been identified in exons 6, 10, 11, 12, 15, and 17. Seventy‐five percent of germline variations are frameshift deletions or insertions (54%), nonsense variations (24%), missense variations (15%), or splice site variations (7%). Twenty five percent of patients with HPT‐JT are reported to have defects in the promoter regions of CDC73 , whole exon, gene deletions, or epigenetic modifications. Note that missense mutations are less associated with the classic phenotype than truncating variants (Newey et al.,  2010 ). The variation found in our study is a frameshift variant located in exon 7 that is a frequent situation. Although this is a common type of variation in a frequently involved exon, it occurs only in nine families in in the literature (Bradley et al.,  2005 ; Carpten et al.,  2002 ; Mehta et al.,  2014 ; Newey et al.,  2010 ; Shattuck et al.,  2003 ; Simonds et al.,  2004 ; Sirbiladze et al.,  2019 ). This variation has been reported previously in 30 patients from nine families. According to phenotypic data from publications, the variant was associated with various clinical presentation, including pHPT (22/22), parathyroid carcinoma (7/30), jaw tumors (1/30), renal lesions (3/30), and uterine lesions in female patients (8/11). These results confirm that the search for a CDC73 mutation should not be based solely on the association of a pHPT with a jaw tumor. It is indicated in particular in the presence of a familial HPT‐JT, in the case of pHPT appearing at a young age (<40 years), of multiglandular involvement, of cystic, atypical or malignant involvement of the parathyroid gland, or in the case of coexistence of an ossifying fibroma of the jaw, of renal or uterine tumors (Table  3 ) (Cetani et al.,  2004 ; Iacobone et al.,  2015 ; van der Tuin et al.,  2017 ). It should be noted that, apart from the family indication, the patient's mother does not meet these criteria. Criteria for searching for CDC73 variations Note : Although the syndrome is called hyperparathyroidism‐jaw tumor, it is not necessary to have a jaw lesion to undertake a CDC73 mutation search. Adenomyosis, characterized by abnormal uterine bleeding, has an overall cumulative incidence and 10 year incidence rate from 2006 to 2015 of approximately 1.03% and 28.9 per 10,000 women per year worldwide (Upson & Missmer,  2020 ). This disorder remains relatively frequent but could lead to the suggestion of a hereditary form in case of association with a pHPT. HPT‐JT syndrome can present in a frustrated way and some families have only uterine manifestations (Koikawa et al.,  2018 ). First‐line surgery of parathyroid gland is recommended given the rarity and phenotypic heterogeneity of CDC73 ‐related disorders, the optimal surgical approach has not yet been established. No benefit for prophylactic parathyroidectomy to prevent malignancy in individuals with germline CDC73 mutation carriers have been demonstrated. The recommended approach should be bilateral exploration to identify and inspect all four glands, with resection only of those that appear abnormal. A bilateral or targeted neck exploration and depending on the result an extensive or limited parathyroidectomy should be performed. Those who do not want to or cannot undergo surgery can be treated with Cinacalcet hydrochloride. Severe hypercalcemia can be treated with zoledronic acid infusion or denosumab (Torresan & Iacobone,  2019 ). In view of the risk of recurrence, patients will be followed according to current guidelines. The follow‐up of patients, aged over 5 years, with CDC73 germline mutations includes a number of tests summarized in Table  4 (Bradley et al.,  2005 ; Torresan & Iacobone,  2019 ). Hyperparathyroidism‐jaw tumor syndrome follow‐up Note : Due to the high risk of parathyroid carcinoma and other disorders, HPT‐JT patients should be monitored regularly. In conclusion, it is important to diagnose these syndromes as they are often associated with serious associated diseases such as parathyroid carcinoma. The value of using an expanded gene panel is confirmed because the absence of associated diseases does not exclude the diagnosis given the high clinical and molecular heterogeneity of these familial hyperparathyroidism syndromes. A rare syndrome due to a rare variation in patients with a priori only isolated pHPT was diagnosed. CDC73 mutations may be more frequent than those described in the literature. Prior to the family study, the mother of our index case had not been diagnosed. It is questionable whether in the context of adenomyosis and hyperparathyroidism >50 years of age, it would be wise to undertake a molecular diagnosis. The current recommendations on variation testing (Table  3 ) only consider associated maxillary lesions. Given the frequency of uterine involvement, it would be sensible to consider including it in the diagnostic criteria. The HPT‐JT syndrome remains extremely rare and reporting of cases remains essential in order to better understand this syndrome and to propose in the future a follow‐up adapted to the patient's genotype allowing personalized medicine.

Not applicable.

Primary hyperparathyroidism (pHPT) is the leading cause of hypercalcemia in ambulatory patients, the second cause overall after cancer, and the third endocrine disorder after diabetes and thyroid disorders (Rao,  2018 ) with a prevalence at 1 to 8.6 per 1000 (Gill et al.,  2006 ; Press et al.,  2013 ; Yeh et al.,  2013 ; Yu et al.,  2009 ) and an incidence at 0.4 to 82 per 100,000 per year (Griebeler et al.,  2015 ; Rao,  2018 ; Walker & Silverberg,  2018 ; Yeh et al.,  2013 ). Monogenic causes account for 5 to 10% of pHPT (Walker & Silverberg,  2018 ) including multiple endocrine neoplasia 1, 2A, and 4 (MEN1, MEN2A, and MEN4), familial isolated hyperparathyroidism (FIHP), neonatal severe primary hyperparathyroidism (NSPHT), familial hypercalcemia hypocalciuria (FHH), and hyperparathyroidism‐jaw tumor (HPT‐JT) (Arnold & Marx,  2013 ; Bilezikian et al.,  2018 ; Carpten et al.,  2002 ; Iacobone et al.,  2015 ; Marx et al.,  2002 ; Rosen et al.,  2018 ; Salcuni et al.,  2018 ; Simonds,  2017 ; Thakker,  2016 ). HPT‐JT is caused by a pathogenic variation in the cell division cycle 73 gene ( CDC73 ; OMIM *607393), also known as hyperparathyroidism 2 with jaw tumors ( HRPT2 ) gene, that encodes parafibromin (for parathyroid tumor and ossifying fibroma (Chen et al.,  2003 ; Digonnet et al.,  2011 )), a ubiquitously expressed protein which acts as a transcriptional regulator as part of a complex associated with RNA polymerase II (Newey et al.,  2010 ). This syndrome is inherited in an autosomal dominant mode. pHPT associated with a variation in the CDC73 gene mainly occurs in adolescence or early adulthood (Bricaire et al.,  2013 ; Pichardo‐Lowden et al.,  2011 ), diagnosed at a median age of 27 years (range 12–58 years) (van der Tuin et al.,  2017 ) and at a mean age of 33 years (range 32–36) (Iacobone et al.,  2015 ); (Hobbs et al.,  1999 ; van der Tuin et al.,  2017 ). HPT‐JT affected patients have a 15 to 20% risk of developing parathyroid carcinoma (Bradley et al.,  2005 ; Cetani et al.,  2016 ; Iacobone et al.,  2015 ) compared to less than 1% in all other cases of pHPT (Digonnet et al.,  2011 ; Hobbs et al.,  1999 ; Walker & Silverberg,  2018 ). HPT‐JT syndrome is also associated with early impairments such as jaw tumors in 30% of cases, kidney abnormalities in 15% of cases (Torresan & Iacobone,  2019 ), and uterine tumors in 50% of affected women. To date no genotype–phenotype correlation has been demonstrated (Iacobone et al.,  2015 ). The aim of this study is to report two atypical cases of HPT‐JT due to a rare variation. The presentation is phenotypically discordant between the index case and his mother. The index case presents with only isolated pHPT without associated disorders. The mother has a late onset pHPT (<50 years) and adenomyosis.

The authors declare no conflict of interest.