Any megalencephaly-polymicrogyria-postaxial polydactyly-hydrocephalus syndrome in which the cause of the disease is a mutation in the PIK3R2 gene. The disease is MONDO_0011313 (megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome 1). Also known as: PIK3R2 megalencephaly-polymicrogyria-postaxial polydactyly-hydrocephalus syndrome, megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome type 1, megalencephaly-polymicrogyria-postaxial polydactyly-hydrocephalus syndrome caused by mutation in PIK3R2.