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. Here, COL1A1 is linked to McCune-Albright syndrome.