Type Description OMIM Gene Type 1a Has a characteristic phenotypic appearance (Albright's hereditary osteodystrophy), including short fourth and fifth metacarpals and a rounded facies. It is most likely an autosomal dominant disorder.[2] It is also associated with thyroid stimulating hormone resistance.[3] 103580 GNAS1 Type 1b Lacks the physical appearance of type 1a, but is biochemically similar.[4] It is associated with a methylation defect.[5][6] 603233 GNAS1, STX16 Type 2 Also lacks the physical appearance of type 1a.[7] Since the genetic defect in type 2 is further down the signalling pathway than in type 1, there is a normal cAMP response to PTH stimulation despite the inherent abnormality in calcium regulation.