Pseudohypoparathyroidism type 1a and the GNAS p.R231H mutation: Somatic mosaicism in a mother with two affected sons.

Pseudohypoparathyrodism (PHP) is a disorder caused by mutations in the guanine nucleotide-binding α-subunit (GNAS). We sought to determine the genetic origin of PHP1a in one affected family. We identified the previously reported Gsα R231H mutation in family members affected with PHP1a. DNA analysis found that the two clinically affected sons are heterozygous for the mutation. The sons have PHP1a, manifesting obesity, intellectual disability, hypogonadism, hypothyroidism and elevated PTH levels. Initial DNA sequencing did not detect the mutation in either parent. However, their mother displayed some features of PHP, including elevated PTH levels and asymmetrical metacarpal shortening. Using molecular cloning, we detected the mutation at low levels in the mother's leukocyte DNA, consistent with somatic mosaicism and her mildly affected status. Thus, we have identified additional cases of PHP1a caused by the Gsα R231H mutation. In this family, the mother has a milder phenotype due in part to somatic mosaicism, whereas the two affected sons have full PHP1a. Though somatic mosaicism for activating GNAS mutations is known to occur in McCune-Albright syndrome, this is the first report confirming somatic mosaicism for a hypofunctioning GNAS mutation in a PHP kindred.