De novo heterozygous missense and loss‐of‐function variants in <i>CDC42BPB</i> are associated with a neurodevelopmental phenotype
Ilana Chilton, Volkan Okur, Giuseppina Vitiello, Angelo Selicorni, Milena Mariani, Alice Goldenberg, Thomas Husson, Dominique Campion, Klaske D. Lichtenbelt, Koen L.I. van Gassen, Michelle Steinraths, Jennifer King Rice, Elizabeth Roeder, Rebecca O. Littlejohn, Myriam Srour, Guillaume Sébire, Andrea Accogli, Delphine Héron, Solveig Heide, Caroline Nava, Christel Depienne, Austin Larson, Dmitriy Niyazov, Meron Azage, George Hoganson, Jennifer Burton, Eric T. Rush, Janda Jenkins, Carol J. Saunders, Isabelle Thiffault, Joseph T. Alaimo, Julie Fleischer, Daniel Groepper, Karen W. Gripp, Wendy K. Chung
Abstract
CDC42BPB encodes MRCKβ (myotonic dystrophy-related Cdc42-binding kinase beta), a serine/threonine protein kinase, and a downstream effector of CDC42, which has recently been associated with Takenouchi-Kosaki syndrome, an autosomal dominant neurodevelopmental disorder. We identified 12 heterozygous predicted deleterious variants in CDC42BPB (9 missense, 2 frameshift, and 1 nonsense) in 14 unrelated individuals (confirmed de novo in 11/14) with neurodevelopmental disorders including developmental delay/intellectual disability, autism, hypotonia, and structural brain abnormalities including cerebellar vermis hypoplasia and agenesis/hypoplasia of the corpus callosum. The frameshift and nonsense variants in CDC42BPB are expected to be gene-disrupting and lead to haploinsufficiency via nonsense-mediated decay. All missense variants are located in highly conserved and functionally important protein domains/regions: 3 are found in the protein kinase domain, 2 are in the citron homology domain, and 4 in a 20-amino acid sequence between 2 coiled-coil regions, 2 of which are recurrent. Future studies will help to delineate the natural history and to elucidate the underlying biological mechanisms of the missense variants leading to the neurodevelopmental and behavioral phenotypes.