Parathyroid tumours, detectable by hypercalcaemia, are usually the first manifestation of the disease and occur in >95% of pa­tients (Fig. 1) (6-26). The underlying aetiology of primary HPT in HPT-JT is usually a solitary parathyroid adenoma but multigland disease may also occur and the frequency of parathy­roid carcinoma in HPT-JT may be 15% (Fig. 1). These features result in recurrent parathyroid disease, which is common in HPT- JT. The occurrence of recurrent parathyroid disease and the oc­currence of parathyroid tumours in isolation and without any evi­dence of jaw tumours, may cause confusion with other heredi­tary disorders of parathyroid tumours (Table I) such as MEN1, FIHP and familial benign hypercalcaemia (FBH), which is also referred to as familial hypocalciuric hypercalcaemia (FHH) and is due to inactivating mutations of the calcium sensing receptor (CaSR). HPT-JT can be distinguished from FBH, because in FBH serum calcium levels are elevated during the early neonatal or infantile period, whereas in HPT-JT such elevations are un­common in the first decade. In addition, HPT-JT patients, in con­trast to FBH patients have associated hypercalciuria. The dis­tinction between HPT-JT patients and MEN1 patients, who have developed only the first manifestation of hypercalcaemia (>90% of patients), is more difficult and is likely to be influenced by op­erative and histologic findings and by the subsequent occur­rence of other characteristic lesions in each disorder. It is important to note that HPT-JT patients usually have single ade­nomas or a carcinoma, whereas MEN1 patients often have multiglandular parathyroid disease. The distinction between FIHP and HPT-JT in the absence of jaw tumours is difficult but important because HPT-JT patients may be at a higher risk of developing parathyroid carcinomas. These distinctions may be helped by the identification of additional features, and a search for jaw tumours, renal and uterine abnormalities (Fig. 1) may help to identify HPT-JT patients.

Ossifying jaw-tumours

The prevalence of ossifying fibromas of the jaw has been report­ed to range from >25% to 50% (Fig. 1), and these may appear as early as 13 years of age. The ossifying fi­bromas are histologically different from the osteoclastic ‘brown’ tumours of primary HPT and do not regress following curative parathyroid surgery. These ossifying fibromas may occa­sionally occur in other bones, and a search for these at sites oth­er than the jaw may help to distinguish between those patients with HPT-JT and FIHP. Ossifying fibromas are an important dis­tinguishing feature of HPT-JT from FIHP and the occurrence of these occasionally may precede the development of hypercal- caemia in HPT-JT patients by several decades.

Renal abnormalities

Renal lesions have been reported with varying frequencies in HPT-JT patients and include Wilms’ tumour, renal hamar­tomas, renal cell carcinomas, renal cortical adenomas and multiple renal cysts. Our analysis (Fig. 1) of the published reports indicates that renal abnor­malities occur in approximately 16% of HPT-JT patients, with proven germline HRPT2 mutations, and that >75% of these ab­normalities consisted of multiple cysts. Only 2 patients were re­ported to develop end stage renal failure. The oc­currence of other renal abnormalities has been reported in only 1 or 2 patients. Thus, Wilms’ tumour has been reported in 2 unrelated patients, renal hamartomas have been re­ported in 4 patients from one family, and renal cell car­cinoma and multiple cortical adenomas in 1 patient.
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