From the Division of Genetics and Genomics, Manton Center for Orphan Disease Research, Howard Hughes Medical Institute (S.S.J., A.-T.N.L., A.M.D., B.J.B., X.Z., R.S.H., J.N.P., A.R., S.S., B.K.M., T.W.Y., C.A.W.), and the Departments of Laboratory Medicine (J.W., Y.S., B.L.W.) and Neurology (M.S., A.P.), Boston Children's Hospital, the Departments of Pediatrics (S.S.J., A.-T.N.L., A.M.D., B.J.B., X.Z., R.S.H., J.N.P., A.R., S.S., B.K.M., T.W.Y., C.A.W.), Neurology (S.S.J., A.-T.N.L., A.M.D., B.J.B., X.Z., R.S.H., J.N.P., A.R., S.S., B.K.M., T.W.Y., C.A.W., M.S., A.P.), and Pathology (Y.S., B.L.W.), Harvard Medical School, the Department of Neurology, Beth Israel Deaconess Medical Center (B.S.C.), and the Department of Neurology, Massachusetts General Hospital (T.W.Y.) - all in Boston; the Department of Paediatrics, KK Women's and Children's Hospital, Singapore, Singapore (S.S.J.); the Department of Genome Sciences, University of Washington, Seattle (M.K., M.B., D.A.N., J.S.); the Department of Laboratory Medicine, Shanghai Children's Medical Center, Shanghai (J.W., Y.S.); the Division of Neurology, Department of Pediatrics, Hacettepe University School of Medicine, Sihhiye, Ankara, Turkey (M.T.); the Neurogenetics Unit, Montreal Neurological Hospital and Institute, Department of Neurology and Neurosurgery (D.A., E.A.) and Department of Human Genetics (E.A.), McGill University, Montreal; the Department of Neurology, Hôpital Universitaire des Enfants Reine Fabiola, Université Libre de Bruxelles, Brussels (B.D.); the Pediatric Neurology Unit and Laboratories, Children's Hospital A. Meyer-University of Florence, Florence, Italy (E.P., R.G.); the Department of Medicine, University of Melbourne, Austin Health, Heidelberg (I.E.S., S.F.B.), Department of Paediatrics, Royal Children's Hospital, University of Melbourne, and the Florey Institute of Neuroscience and Mental Health, Melbourne (I.E.S.), and the Department of Neurology, Royal Children's Hospital, Murdoch Children'
Although there is increasing recognition of the role of somatic mutations in genetic disorders, the prevalence of somatic mutations in neurodevelopmental disease and the optimal techniques to detect somatic mosaicism have not been systematically evaluated.
Using a customized panel of known and candidate genes associated with brain malformations, we applied targeted high-coverage sequencing (depth, ≥200×) to leukocyte-derived DNA samples from 158 persons with brain malformations, including the double-cortex syndrome (subcortical band heterotopia, 30 persons), polymicrogyria with megalencephaly (20), periventricular nodular heterotopia (61), and pachygyria (47). We validated candidate mutations with the use of Sanger sequencing and, for variants present at unequal read depths, subcloning followed by colony sequencing.
Validated, causal mutations were found in 27 persons (17%; range, 10 to 30% for each phenotype). Mutations were somatic in 8 of the 27 (30%), predominantly in persons with the double-cortex syndrome (in whom we found mutations in DCX and LIS1), persons with periventricular nodular heterotopia (FLNA), and persons with pachygyria (TUBB2B). Of the somatic mutations we detected, 5 (63%) were undetectable with the use of traditional Sanger sequencing but were validated through subcloning and subsequent sequencing of the subcloned DNA. We found potentially causal mutations in the candidate genes DYNC1H1, KIF5C, and other kinesin genes in persons with pachygyria.
Targeted sequencing was found to be useful for detecting somatic mutations in patients with brain malformations. High-coverage sequencing panels provide an important complement to whole-exome and whole-genome sequencing in the evaluation of somatic mutations in neuropsychiatric disease. (Funded by the National Institute of Neurological Disorders and Stroke and others.).