GNAS and McCune-Albright syndrome: These include osteogenesis imperfecta type 1 caused by Col1A1 and Col1A2 mutations, infantile hypophoshatasia caused by inactivating mutations of ALP, and McCune-Albright syndrome caused by activating mutations of GNAS1.(8) It will be interesting to determine if gene polymorphisms of GPRC6A are associated with osteopenic and hypercalciuric clinical disorders.