PIK3R2 and megalencephaly: In addition, somatic activating phosphatidylinosiltol-4,5-bisphosphate 3-kinase, catalytic subunit alpha (PIK3CA) mutations and germline activating phosphoinositide-3-kinase, regulatory subunit 2 (beta) (PIK3R2) mutations (both encoding PI3K regulatory subunits) cause conditions characterized by increased head circumference; megalencephaly-capillary malformation (MCAP [MIM 602501]) and megalencephaly-polymicrogyria-polydactyly-hydrocephalus (MPPH [MIM 603387]) syndromes, respectively (10).