Diagnóstico molecular de formas familiares de hipercalcémia

The hypersecretion of parathormone (PTH), associated to hypercalcemia, is an endocrinopathy designated as primary hyperparathyroidism (HPT), which may result from the hyperactivity of adenomas (80-85%), hyperplasia (15-20%) or carcinomas (about 1 %) of the parathyroid glands. Primary hyperparathyroidism usually occurs sporadically, however, approximately 10% of the patients present a familial form. The aim of the present study was to identify and characterize germ line mutations in the CaSR, HRPT2 and MEN1 genes, which are involved in familial forms of hypercalcemia, respectively, familial hypocalciuric hypercalcemia (FHH)/neonatal severe hyperparathyroidism (NSHPT), hyperparathyroidism-jaw tumour (HPT-JT), and multiple endocrine neoplasia type 1 (MEN1). Ten probands and nineteen relatives were studied. Sequencing analysis of the CaSR gene revealed two novel mutations (Arg69His and c.1945delG) and one previously described (Arg680His), in two families and one case with no family history, with FHH/NSHPT. In two cases presenting parathyroid tumours, with no family history of the disease, two novel germ line mutations in the HRPT2 gene (Arg76stop and c.518del4bp) were identified, suggesting that the parathyroid lesions represented an incomplete expression of HPT-JT syndrome. The detection of a somatic HRPT2 mutation (Leu5Pro) in the parathyroid carcinoma of a patient carrying a germ line mutation in this gene, confirmed the total inactivation and the oncosupression function of the HRPT2 gene. Segregation studies, using microsatellites markers, in two new individuals, from a previously studied family with a large deletion in the MEN1 gene, del (exon 7 3' non translated region), revealed that these individuals did not have inherited the haplotype associated to the mutant allele. The study developed in the present thesis, allowed the early identification of ten individuals carrying germ line mutations in genes involved in familial hypercalcemia and contributed to a better understanding of molecular mechanisms involved in parathyroid tumorigenesis