Identification and characterization of two new, highly polymorphic loci adjacent to GNAS1 on chromosome 20q13.3.

GNAS1, which is located in the chromosomal region 20q13.3, gives rise to maternally, paternally or bi-allelically expressed transcripts including the one that encodes the alpha subunit of the stimulatory G protein. Numerous naturally occurring mutations of this gene have been identified in several different disorders including certain forms of pseudohypoparathyroidism, progressive osseous heteroplasia, McCune-Albright syndrome and acromegaly. Polymorphic markers currently employed in the genetic evaluation of these disorders frequently prove uninformative owing to a low heterozygosity value associated with each marker. We searched for potentially polymorphic tandem repeats close to the GNAS1 locus, and identified two new, highly polymorphic loci that are located within a;48-kb region immediately downstream of this gene. These new microsatellite markers, with their high polymorphism information content, may prove to be useful in genetic studies related to GNAS1 as well as to other genes located in the flanking genomic region.