Novel mutations of the calcium-sensing receptor impede differential diagnosis of primary hyperparathyroidism and familial hypocalciuric hypercalcemia.

Abstract

Familial hypocalciuric hypercalcemia 1 (FHH1) is an autosomal dominant disorder caused by inactivating mutations in the calcium-sensing receptor (CaSR) gene, commonly leading-in contrast to primary hyperparathyroidism (PHPT)-to asymptomatic hypercalcemia. It is important to establish the correct diagnosis, as surgery may be curative in PHPT, but most likely ineffective in FHH. The study aims to evaluate patients with FHH1, initially misinterpreted as PHPT and some even undergone surgery. CaSR-genotyping was conducted, various biochemical parameters including twenty-four-hour urinary Ca excretion (24hU CE) and the calculated relation of urinary Ca clearance to creatinine clearance (CCCR), type of surgery and 1-year follow-up data of fourteen patients with proven FHH1 were evaluated retrospectively. Genetic analysis revealed a total of nine novel heterozygous variants in the CaSR gene in our study population. Six of fourteen patients (42.9%) underwent surgery for initially suspected PHPT, showing normalized biochemical parameters immediately after surgery. In 1-year follow-up, however, five of six operated patients (83.3%) showed normal parathyroid hormone (PTH), but elevated serum calcium levels. In contrast, only one of the operated patients (16.7%) presented both PTH and serum calcium in the normal range. Histology showed adenoma in three (50%), hyperplasia in two (33.3%), and normal parathyroid tissue in one (16.7%) of the patients. We discovered novel heterozygous variants in the CaSR gene, which considerably impede differential diagnosis of PHPT and FHH1. Furthermore, our results indicate that parathyroid surgery fails to provide long-term benefits for patients with FHH1 and suspected PHPT, even though this coincidence seems to exist.