Megalencephaly-polymicrogyria-polydactyly-hydrocephalus (MPPH) is a developmental brain disorder characterized by megalencephaly and bilateral perisylvian polymicrogyria due to defects in genes of the PI3K-AKT pathway.
Our case highlights the importance of considering PI3K-AKT-mTOR pathway variants as a cause for megalencephaly and cortical malformation when the phenotype includes hypoglycaemia.
Alterations of the PI3K/Akt/mammalian target of rapamycin complex 1 (mTORC1) signaling pathway are causally involved in a subset of malformations of cortical development (MCDs) ranging from focal cortical dysplasia (FCD) to hemimegalencephaly and megalencephaly.
Mutations of genes within the phosphatidylinositol-3-kinase (PI3K)-AKT-MTOR pathway are well known causes of brain overgrowth (megalencephaly) as well as segmental cortical dysplasia (such as hemimegalencephaly, focal cortical dysplasia and polymicrogyria).
Yet, prevalence of the involvement of the PI3K-AKT-mTOR pathway in patients with megalencephaly remains to be elucidated, and molecular diagnosis is challenging.
These observations suggest that cyclin D2 stabilization, caused by CCND2 mutation or PI3K-AKT activation, is a unifying mechanism in PI3K-AKT-related megalencephaly syndromes.