Definition An autosomal dominant disorder (OMIM:603387) characterised by megalencephaly, hydrocephalus, and polymicrogyria and variably present polydactyly
Differential diagnosis Megalencephaly-capillary malformation syndrome
Molecular pathology Defects of
• AKT3, which encodes protein kinase B, an AKT serine-threonine protein kinase,
• PIK3CA, which encodes the catalytic subunit of PI3-kinase, which uses ATP to phosphorylate phosphatidylinositol, phosphatidylinositol4P and phosphatidylinositol(4,5)P2, and
• PIK3R2, which encodes a regulatory subunit of PI3-kinase, that acts as an adapter, mediating the association of the p110 catalytic unit to the plasma membrane, all cause megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome.
Synonyms Megalencephaly—polymicrogyria—mega corpus callosum syndrome, MEG-PMG-MEGACC syndrome, megalencephaly—mega corpus callosum—and complete lack of motor development