Albright hereditary osteodystrophy also known as pseudohypoparathyroidism type 1A (PHP1a) is a type of pseudohypoparathyroidism characterized by renal resistance to parathyroid hormone (PTH), resulting in hypocalcemia, hyperphosphatemia, and elevated PTH; resistance to other hormones including thydroid stimulating hormone (TSH), gonadotropins and growth-hormone-releasing hormone (GHRH); and a constellation of clinical features.
In about 70-80% of cases, PHP-Ia is caused by haploinsufficiency due to maternally-inherited heterozygous inactivating mutations in the GNAS gene (20q13). In a subset of patients negative for these mutations, methylation defects at the same locus have been reported.
