GNAS and progressive osseous heteroplasia: Based on the type of GNAS defect, five subtypes of PHP can be distinguished: type 1A (PHP1A, maternal inactivating mutations or de novo mutations) OMIM#103580; type 1B (PHP1B, imprinting dysregulation) OMIM#603233; type 1C (PHP1C, few inactivating mutations at the last amino acids reported) OMIM#612462; pseudopseudohypoparathyroidism (PPHP) OMIM#612463 and progressive osseous heteroplasia (POH) OMIM#166350 (both characterized by paternal inactivating mutations or de novo mutations).