Mutations specific to the Rac-GEF domain of TRIO cause intellectual disability and microcephaly

Reuben J. Pengelly, Stephanie Greville-Heygate, Susanne Schmidt, Eleanor G. Seaby, M. Reza Jabalameli, Sarju G. Mehta, Michael J. Parker, David Goudie, Christine Fagotto-Kaufmann, Catherine Mercer, Anne Debant, Sarah Ennis, Diana Baralle (Lead / Corresponding author)

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    Abstract

    Background Neurodevelopmental disorders have challenged clinical genetics for decades, with over 700 genes implicated and many whose function remains unknown. The application of whole-exome sequencing is proving pivotal in closing the genotype/phenotype gap through the discovery of new genes and variants that help to unravel the pathogenic mechanisms driving neuropathogenesis. One such discovery includes TRIO, a gene recently implicated in neurodevelopmental delay. Trio is a Dbl family guanine nucleotide exchange factor (GEF) and a major regulator of neuronal development, controlling actin cytoskeleton dynamics by activating the GTPase Rac1. 

    Methods Whole-exome sequencing was undertaken on a family presenting with global developmental delay, microcephaly and mild dysmorphism. Father/daughter exome analysis was performed, followed by confirmatory Sanger sequencing and segregation analysis on four individuals. Three further patients were recruited through the deciphering developmental disorders (DDD) study. Functional studies were undertaken using patient-specific Trio protein mutations. 

    Results We identified a frameshift deletion in TRIO that segregated autosomal dominantly. By scrutinising data from DDD, we further identified three unrelated children with a similar phenotype who harboured de novo missense mutations in TRIO. Biochemical studies demonstrated that in three out of four families, the Trio mutations led to a markedly reduced Rac1 activation. 

    Conclusions We describe an inherited global developmental delay phenotype associated with a frameshift deletion in TRIO. Additionally, we identify pathogenic de novo missense mutations in TRIO associated with the same consistent phenotype, intellectual disability, microcephaly and dysmorphism with striking digital features. We further functionally validate the importance of the GEF domain in Trio protein function. Our study demonstrates how genomic technologies are yet again proving prolific in diagnosing and advancing the understanding of neurodevelopmental disorders.

    Original languageEnglish
    Pages (from-to)735-742
    Number of pages8
    JournalJournal of Medical Genetics
    Volume53
    Issue number11
    Early online date14 Jul 2016
    DOIs
    Publication statusPublished - 1 Nov 2016

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  • Cite this

    Pengelly, R. J., Greville-Heygate, S., Schmidt, S., Seaby, E. G., Jabalameli, M. R., Mehta, S. G., Parker, M. J., Goudie, D., Fagotto-Kaufmann, C., Mercer, C., Debant, A., Ennis, S., & Baralle, D. (2016). Mutations specific to the Rac-GEF domain of TRIO cause intellectual disability and microcephaly. Journal of Medical Genetics, 53(11), 735-742. https://doi.org/10.1136/jmedgenet-2016-103942