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Case Reports
. 2017 Nov 9:8:59.
doi: 10.1186/s13229-017-0175-3. eCollection 2017.

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

Marc Woodbury-Smith  1   2 , Eric Deneault  2 , Ryan K C Yuen  2 , Susan Walker  2 , Mehdi Zarrei  2 , Giovanna Pellecchia  2 , Jennifer L Howe  2 , Ny Hoang  3   4 , Mohammed Uddin  5 , Christian R Marshall  2 , Christina Chrysler  6 , Ann Thompson  6 , Peter Szatmari  4 , Stephen W Scherer  2   7   8
Affiliations
Case Reports

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

Marc Woodbury-Smith et al. Mol Autism. .

Abstract

Background: 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 RAB39B segregates with ASD phenotype.

Methods: 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.

Results: Two males with an inherited RAB39B 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 RAB39B revealed an impact on expression in differentiated neurons for several genes implicated in brain development and function, supported by our pathway enrichment analysis.

Conclusions: Penetrance for ASD is high among males but more variable among females with RAB39B mutations. A critical role for this gene in brain development and function is demonstrated.

Keywords: Intellectual disability (ID); RAB39B; RNAseq; Whole genome sequencing (WGS).

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Conflict of interest statement

Ethics approval and consent to participate

All data were collected following informed consent from participants or substitute decision-makers, and the study was conducted with approval from the Hospital for Sick Children, Toronto, local research ethics board.

Consent for publication

The mother has provided specific written consent for this case report using the Hospital for Sick Children consent form.

Competing interests

The authors declare no conflict of interest for the contents of the data in this study.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1
Fig. 1
Annotated pedigree of family described in the text
Fig. 2
Fig. 2
Levels of transcript of selected genes in control and RAB39B-/γ-glutaminergic neurons as determined by RNAseq experiment. Values are presented as mean ± SD of four (RAB39B) and six (control) independent experiments
Fig. 3
Fig. 3
Literature curation for RAB39B mutations
See this image and copyright information in PMC

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