PIK3CA and megalencephaly: To date, the association of macrocephaly with polydactyly has been observed in a range of disorders, including megalencephaly-polydactyly-polymicrogyria-hydrocephalus (MPPH; MIM: 615938), due to stabilizing mutations in CCND2,17 and megalencephaly-capillary malformation (MCAP; MIM: 602501) due to mutations of the PI3K-AKT-mTOR pathway upstream of CCND2.26