Megalencephaly-capillary malformation (MCAP) and megalencephaly- polymicrogyria-polydactyly-hydrocephalus (MPPH) syndromes are sporadic overgrowth disorders associated with markedly enlarged brain size and other recognizable features. We performed exome sequencing in 3 families with MCAP or MPPH, and our initial observations were confirmed in exomes from 7 individuals with MCAP and 174 control individuals, as well as in 40 additional subjects with megalencephaly, using a combination of Sanger sequencing, restriction enzyme assays and targeted deep sequencing. We identified de novo germline or postzygotic mutations in three core components of the phosphatidylinositol 3-kinase (PI3K)-AKT pathway. These include 2 mutations in AKT3, 1 recurrent mutation in PIK3R2 in 11 unrelated families with MPPH and 15 mostly postzygotic mutations in PIK3CA in 23 individuals with MCAP and 1 with MPPH. Our data highlight the central role of PI3K-AKT signaling in vascular, limb and brain development and emphasize the power of massively parallel sequencing in a challenging context of phenotypic and genetic heterogeneity combined with postzygotic mosaicism.
Bibliographical noteFunding Information:
This work was funded by the US National Institutes of Health under National Institute of Neurological Disorders and Stroke (NINDS) grant NS058721 (to W.B.D.), National Institute of Child Health & Human Development (NICHD) grant HD36657 and National Institute of General Medical Sciences (NIGMS) grant 5-T32-GM08243 (to J.M.G.), the Government of Canada (to FORGE) through Genome Canada, the Canadian Institutes of Health Research (CIHR) and the Ontario Genomics Institute (OGI-049). Additional funding was provided to FORGE by Genome Quebec and Genome British Columbia. J.-B.R. is supported by a Banting Postdoctoral Fellowship from the CIHR. K.M.B. is supported by a Clinical Investigatorship Award from the CIHR Institute of Genetics. The laboratory of M.O. is funded by Cancer Research UK (CR-UK), the Medical Research Council (UK) and Leukaemia Lymphoma Research (UK). M.O. is a Senior CR-UK Research Fellow. We would like to thank the Simons Foundation Autism Research Initiative (SFARI) for providing control exome data (grant 191889 to J.S.). We also thank the NIEHS Environmental Genome Project (contract HHSN273200800010C) and the NHLBI GO Exome Sequencing Project and its ongoing studies—Lung GO (HL-102923), Broad GO (HL-102925), Seattle GO (HL-102926), Heart GO (HL-103010) and the Women’s Health Institute (WHI; HL-102924) Sequencing Projects—for providing exome variant calls for comparison.