A rare genetic neurodevelopmental disorder characterized by neonatal hypotonia, global developmental delay, normal to accelerated growth, absent to severely delayed speech, and minor dysmorphic features. Phelan-McDermid syndrome can be caused by a deletion at chromosome 22q13 or by mutation in the SHANK3 gene. The disease is Monarch Disease Ontology entry MONDO_0011652 (Phelan-McDermid syndrome). Also known as: PHMDS, Phelan McDermid syndrome.