GNAS1 MUTATIONAL ANALYSIS IN PSEUDOHYPOPARATHYROIDISM

OBJECTIVE Mutations of the GNAS1 gene, which is located on chromosome 20q13.11 and encodes the alpha-subunit of the stimulatory GTP-binding protein, have been identified in patients with pseudohypoparathyroidis m type Ia (PHPIa) and pseudopseudohypoparathyroidism (PPHP), We have u ndertaken studies to determine the prevalence of GNAS1 mutations and t o explore methods for their more rapid detection. METHODS Thirteen unr elated families (8 with PHPIa and PPHP patients, and 5 with PPHP patie nts only) were investigated for GNAS1 mutations in the 1050 base-pair (bp) region spanning exons 2-13 by single-stranded conformational poly morphism (SSCP) and DNA sequence analysis, RESULTS GNAS1 mutations wer e detected in 4 of the 8 families with PHPIa patients. These consisted of: two novel de novo missense mutations (Pro115Ser and Glu259Val) in two families and an identical 4 bp deletion of codons 189 and 190 res ulting in a frameshift in two unrelated families. These results expand the spectrum of GNAS1 mutations associated with this disorder and con firm the presence of a mutational hot-spot involving codons 189 and 19 0, SSCP analysis was found to be a specific and sensitive method that detected all 4 mutations, GNAS1 mutations were not detected in any of the PPHP only families. CONCLUSIONS The pseudohypoparathyroid disorder s appear to represent a heterogeneous group with GNAS1 mutations formi ng the molecular aetiology in approximately 50% of pseudohypoparathyro idism type la families. Such mutations can be reliably identified by s ingle-stranded conformational polymorphism and this will help to suppl ement the clinical evaluation of some patients and their families, par ticularly as the disease may not be fully penetrant.