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.
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.
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).
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.
Yet, prevalence of the involvement of the PI3K-AKT-mTOR pathway in patients with megalencephaly remains to be elucidated, and molecular diagnosis is challenging.
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.