Mutations in RAB39B in individuals with intellectual disability, autism spectrum disorder, and macrocephaly

• Published in: Molecular autism Vol. 8; no. 1; pp. 59 - 10
• Main Authors: Woodbury-Smith, Marc, Deneault, Eric, Yuen, Ryan K. C., Walker, Susan, Zarrei, Mehdi, Pellecchia, Giovanna, Howe, Jennifer L., Hoang, Ny, Uddin, Mohammed, Marshall, Christian R., Chrysler, Christina, Thompson, Ann, Szatmari, Peter, Scherer, Stephen W.
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 09.11.2017; BioMed Central; BMC
• Subjects: Alleles; Analysis; Autism Spectrum Disorder - complications; Autism Spectrum Disorder - diagnosis; Autism Spectrum Disorder - genetics; Care and treatment; Cells, Cultured; Child; Codon, Nonsense; CRISPR-Cas Systems - genetics; Diagnosis; Disabilities; DNA sequencing; Female; Fibroblasts - cytology; Genetic aspects; Genotype; Health aspects; Humans; Induced Pluripotent Stem Cells - cytology; Induced Pluripotent Stem Cells - metabolism; Intellectual disability (ID); Intellectual Disability - complications; Intellectual Disability - diagnosis; Intellectual Disability - genetics; Macrocephaly; Male; Megalencephaly - complications; Megalencephaly - diagnosis; Megalencephaly - genetics; Mutation; Pedigree; Pervasive developmental disorders; Phenotype; rab GTP-Binding Proteins - deficiency; rab GTP-Binding Proteins - genetics; RAB39B; RNA sequencing; RNAseq; Whole Genome Sequencing; Whole genome sequencing (WGS); RAB39B; Whole genome sequencing (WGS); Intellectual disability (ID); RNAseq
• ISSN: 2040-2392; 2040-2392
• DOI: 10.1186/s13229-017-0175-3

Autism spectrum disorder (ASD), a developmental disorder of early childhood onset, affects males four times more frequently than females, suggesting a role for the sex chromosomes. In this study, we describe a family with ASD in which a predicted pathogenic nonsense mutation in the X-chromosome gene segregates with ASD phenotype. Clinical phenotyping, microarray, and whole genome sequencing (WGS) were performed on the five members of this family. Maternal and female sibling X inactivation ratio was calculated, and phase was investigated. Mutant-induced pluripotent stem cells engineered for an exon 2 nonsense mutation were generated and differentiated into cortical neurons for expression and pathway analyses. Two males with an inherited mutation both presented with macrocephaly, intellectual disability (ID), and ASD. Their female sibling with the same mutation presented with ID and a broad autism phenotype. In contrast, their transmitting mother has no neurodevelopmental diagnosis. Our investigation of phase indicated maternal preferential inactivation of the mutated allele, with no such bias observed in the female sibling. We offer the explanation that this bias in X inactivation may explain the absence of a neurocognitive phenotype in the mother. Our cellular knockout model of revealed an impact on expression in differentiated neurons for several genes implicated in brain development and function, supported by our pathway enrichment analysis. Penetrance for ASD is high among males but more variable among females with mutations. A critical role for this gene in brain development and function is demonstrated.