[Clinical features of two cases of pseudohypoparathyroidism (ia and ib) and molecular analysis of GNAS].

Pseudohypoparathyroidism (PHP) is a rare disorder, characterized by a tissue resistance to parathyroid hormone (PTH). The two main subtypes of PHP, PHPIa and PHPIb, are caused by alterations in the GNAS locus (20q13.3), which encodes the Gsα protein, essential for the action of PTH and other hormones. PHP-Ia is associated with several hormone resistances, Albright hereditary osteodystrophy (AHO), and reduced Gsα activity. It is caused by inactivating mutations in the GNAS gene. PHP-Ib presents with isolated resistance to PTH, without AHO and with normal to low Gsα activity. It is related to imprinting defects in GNAS. Two unrelated cases of PHP-Ia and PHP-Ib are presented here, focusing on their clinical aspects and in the differential diagnosis with similar pathologies.