MEF2C and Pitt-Hopkins syndrome: Pitt-Hopkins syndrome (PTHS, MIM# 610954), MEF2C-related intellectual disability (MRD20; MIM# 613443), Mowat-Wilson syndrome (MOWS, MIM# 235730), ATRX-related intellectual disability (ATRX, MIM#301040; MRXHF1, MIM#309580) and Angelman syndrome (AS, MIM#105830) represent a particular group of syndromic NDDs.