The megalencephaly-polymicrogyria-polydactyly-hydrocephalus (MPPH) syndrome characterized by:
- Megalencephaly (MEG) – often congenital
- Polymicrogyria
- Hydrocephalus – may require neurosurgical intervention
- Polydactyly – typically postaxial polydactyly
Mutations are most often heterozygous de novo.