PDE4D and 2q37 microdeletion syndrome: Mutations in regions different from 20q were reported in small subsets of clinically diagnosed PHP patients with no detectable GNAS defects, highlighting the clinical overlap with diseases in the differential diagnosis of PHP: acrodysostosis (ACRDYS, PRKAR1A and PDE4D genes, MIM#101800 and #614316, respectively) and brachydactyly mental retardation syndrome (BDMR, also known as AHO-like syndrome or 2q37 microdeletion syndrome, MIM#600430) [5, 17].