HPT-JT Syndrome
Primary hyperparathyroidism. Individuals with primary hyperparathyroidism may be asymptomatic or may present with nephrolithiasis, reduced bone mass, fracture, fatigue, muscle weakness, bone or joint pain, and/or constipation.
Primary hyperparathyroidism occurs in up to 95% of individuals with HPT-JT syndrome. The onset is typically in late adolescence or early adulthood and is often the first feature of HPT-JT syndrome [Figueiredo et al 2023, Tora et al 2023]. The youngest reported individual with hypercalcemia was age seven years [Pichardo-Lowden et al 2011]. The median age of diagnosis reported in more recent studies has ranged from 23 years to 38 years [Bricaire et al 2013, van der Tuin et al 2017, Iacobone et al 2020, Tora et al 2023].
Penetrance increases with age: in a Dutch population the penetrance of primary hyperparathyroidism in individuals with HPT-JT syndrome at ages 25, 50, and 70 years was reported to be 8%, 53%, and 75%, respectively [van der Tuin et al 2017], while an Italian study of five kindreds showed 68% penetrance in those older than age 30 years [Iacobone et al 2020].
In most individuals with HPT-JT syndrome, hyperparathyroidism is caused by a single benign parathyroid adenoma, which is often cystic or has atypical histologic features. Pathology of parafibromin-deficient parathyroid tumors may show distinct morphology, including microcystic features, sheet-like morphology, eosinophilic cytoplasm, nuclear enlargement with coarse chromatin, prominent vascularity, and a thickened capsule [Gill et al 2019, Erickson et al 2022].
Many families segregating a CDC73 pathogenic variant have at least one affected member with a cystic, malignant, and/or atypical parathyroid tumor. A second parathyroid tumor may occur synchronously or metachronously months to decades after appearance of the first tumor. Analysis of 20 individuals showed single-gland disease in 95%, with 23.5% of these individuals experiencing metachronous recurrence in a second gland; the disease-free interval ranged from five to 27 years [Iacobone et al 2020]. Similarly, a series of 20 individuals showed 25% rate of recurrence of primary hyperparathyroidism [Figueiredo et al 2023].
In at least 10%-15% of individuals with HPT-JT syndrome, primary hyperparathyroidism is caused by parathyroid carcinoma. Two recent studies of individuals with HPT-JT syndrome and primary hyperparathyroidism identified that 31% (17/55) and 23.5% (4/17) had parathyroid carcinoma [Figueiredo et al 2023, Tora et al 2023]. The earliest reported diagnosis of parathyroid carcinoma was age eight years in a girl with pulmonary metastases [Davidson et al 2016]. However, onset may be delayed until the sixth decade [van der Tuin et al 2017, Iacobone et al 2020]. Nonfunctioning parathyroid carcinomas have also been reported [Guarnieri et al 2006].
Jaw tumors. Ossifying fibromas of the mandible or maxilla, also known as cementifying fibromas and cemento-ossifying fibromas, occur in 11%-40% of individuals with HPT-JT syndrome [Bricaire et al 2013, Torresan & Iacobone 2019, Tora et al 2023]. Some ossifying fibromas present as an enlarging visible or palpable mass, whereas others are only detected on dental x-ray. Although benign, these tumors can disrupt normal dentition, impair breathing, and be of significant cosmetic concern. Tumors may occasionally be bilateral/multifocal and may recur. The tumors are considered aggressive and continue to enlarge if not treated.
The frequency of CDC73 pathogenic variants in individuals with ossifying fibromas of the jaw has not been extensively studied. Pimenta et al [2006] found a heterozygous germline pathogenic variant in one of three individuals with an ossifying fibroma of the mandible and no family history, but not in an individual with a juvenile ossifying fibroma of the mandible without a family history. Haag et al [2008] and Kutcher et al [2013] reported individuals with heterozygous germline CDC73 pathogenic variants who had an ossifying fibroma and later developed primary hyperparathyroidism. Chen et al [2016] reported 19 children and 21 adults with sporadic ossifying fibromas, none of whom had a germline CDC73 pathogenic variant identified by sequence analysis (deletion/duplication analysis was not performed); two individuals had somatic CDC73 pathogenic variants confined to the ossifying fibroma.
The specific features of jaw tumors associated with HPT-JT syndrome have not been well defined; in fact, pathologists disagree on the nomenclature used to classify benign fibro-osseous lesions. Most jaw tumors in HPT-JT syndrome are reported as ossifying fibromas or cementifying fibromas that occur in molar or premolar areas [Chen et al 2003], most often appear to be radiographically radiolucent, and usually develop prior to the third decade of life. Sporadic cemento-ossifiyng fibromas may appear as radiolucent or mixed radiolucent/radiopaque lesions, have a female preponderance, and typically develop after the third decade of life [Szabó et al 1995, Aldred et al 2006, Soluk-Tekkesin & Wright 2022].
Juvenile fibromas are histologic variants of ossifying fibromas that, when they occur sporadically, tend to occur at a younger mean age than ossifying fibromas. It is not clear if juvenile fibromas are part of HPT-JT syndrome. Of nine sporadic-appearing ossifying fibromas, parafibromin staining was negative in four of seven ossifying and cemento-ossifying fibromas and positive in three juvenile ossifying fibromas, indicating that loss of CDC73 expression may contribute to the development of ossifying fibromas but not juvenile fibromas [Costa-Guda et al 2021].
Of note, the jaw tumors of HPT-JT syndrome are distinct from the "brown" tumors/osteoclastomas associated with severe hyperparathyroidism (osteitis fibrosa cystica) and do not resolve following curative parathyroidectomy.
Kidney manifestations. Approximately 15%-20% of individuals with HPT-JT syndrome have kidney lesions, most commonly cysts; renal hamartomas and (more rarely) Wilms tumor, including adult-onset Wilms tumor, have also been reported [Torresan & Iacobone 2019].
Kidney cystic disease is variable and ranges from a few minor cysts to bilateral polycystic disease presenting with end-stage kidney disease [Tan & Teh 2004]. Cysts have also been observed in association with rare solid tumors, which were histologically similar to mixed epithelial-stromal tumors or adult mesoblastic nephroma (described in one family), or hamartomatous-type tumors [Teh et al 1996, Tan & Teh 2004]. Three individuals with a CDC73 pathogenic variant from one family had mixed epithelial and stromal tumors [Vocke et al 2019].
Renal malignancy is rare in individuals with HPT-JT syndrome. One individual with HPT-JT syndrome had both papillary renal carcinoma and multiple renal cell adenomas [Haven et al 2000]. Wilms tumor has been reported in at least three unrelated families with HPT-JT syndrome, including an individual who developed bilateral Wilms tumor at age 53 years, and a child, age six years, who developed metastatic Wilms tumor with biallelic loss of CDC73 on tumor tissue testing [Kakinuma et al 1994, Szabó et al 1995, Tora et al 2023].
Individuals with HPT-JT syndrome may be at risk for multiple bilateral kidney lesions, and nephron-sparing surgery rather than radical kidney resection should be considered [Vocke et al 2019].
Uterine manifestations. Benign uterine tumors appear to be common and can be the presenting manifestation in women with HPT-JT syndrome [Tora et al 2023]. Rare uterine malignancies have also been documented. In one study of HPT-JT syndrome kindreds, uterine pathology was described in women who underwent hysterectomy for menorrhagia [Bradley et al 2005]. The following were identified at time of surgery (average age: 35 years; range: 23-55 years): adenomyosis (8), adenofibroma (5), endometrial hyperplasia (4), leiomyoma (4), and adenosarcoma (2). A similar array of uterine findings and age of diagnosis were described in a more recent series of 32 females, in which 38% developed uterine tumors. In addition to the above pathologies, this series also described cervical polyps in four women, adenomyoma in five women, and adenocarcinoma in one woman [Tora et al 2023]. A 2019 review [Torresan & Iacobone 2019] suggested that 45.1% of women with HPT-JT syndrome reported in the literature were diagnosed with uterine lesions. Women with HPT-JT syndrome may present with menorrhagia and require hysterectomy at a younger than average age. In addition, the observation that women with HPT-JT syndrome have a higher rate of miscarriage than unaffected controls and a lower rate of fertility than both unaffected controls and affected males suggests that uterine tumors may contribute to decreased reproductive fitness of women with HPT-JT syndrome [Bradley et al 2005].
Other tumors. Pancreatic adenocarcinoma, testicular mixed germ cell tumor, and Hürthle cell (oncocytic) thyroid adenoma were reported in individuals from a large kindred with HPT-JT syndrome; colon adenocarcinoma, leukemia, papillary thyroid carcinoma, neurofibroma, and chronic lymphatic leukemia have been reported in other kindreds [Mallette et al 1987, Inoue et al 1995, Haven et al 2000, Iacobone et al 2009]. However, it is not clear that these tumors are present at a higher frequency in individuals with HPT-JT syndrome than in the general population, nor that these tumors were caused by a CDC73 pathogenic variant. A woman with HPT-JT syndrome had an ovarian granulosa cell tumor diagnosed at age 31; however, parafibromin staining was intact on analysis of tumor tissue [Sirbiladze et al 2019].