Analysis of the GNAS1 gene in albright's hereditary osteodystrophy

Albright's hereditary osteodystrophy (AHO) is characterized by phenotypic signs that typically include brachydactyly and sc calcifications occurring with or without hormone resistance toward PTH or other hormones such as thyroid hormone or gonadotropins. Different inactivating mutations of the gene GNAS1 encoding Gsα lead to a reduced Gsα protein activity in patients with AHO and pseudohypoparathyroidism type Ia or without resistance to PTH (pseudopseudohypoparathyroidism). We investigated 29 unrelated patients with AHO and pseudohypoparathyroidism type Ia or pseudopseudohypoparathyroidism and their affected family members performing functional and molecular genetic analysis of Gsα. In vitro determination of Gsα protein activity in erythrocyte membranes was followed by the investigation of the whole coding region of the GNAS1 gene using PCR, nonisotopic single strand conformation analysis, and direct sequencing of the PCR products. AH patients showed a reduced Gsα protein activity (mean 59% compared with healthy controls). In 21/29 (72%) patients, 15 different mutations in GNAS1 including 11 novel mutations were detected. In addition we add five unrelated patients with a previously described 4 bp deletion in exon 7 (Δ GACT, codon 189/ 190), confirming the presence of a hot spot for loss of function mutations in GNAS1. In eight patients, no molecular abnormality was found in the GNAS1 gene despite a functional defect of Gsα. We conclude that biochemical and molecular analysis of Gsα and its gene GNAS1 can be valuable tools to confirm the diagnosis of AHO. However, in some patients with reduced activity of Gsα, the molecular defect cannot be detected in the exons encoding the common form of Gsα.