Activating RAC1 variants in the switch II region cause a developmental syndrome and alter neuronal morphology.

Banka, Siddharth; Bennington, Abigail; Baker, Martin J; Rijckmans, Ellen; Clemente, Giuliana D; Ansor, Nurhuda Mohamad; Sito, Hilary; Prasad, Pritha; Anyane-Yeboa, Kwame; Badalato, Lauren; Dimitrov, Boyan; Fitzpatrick, David; Hurst, Anna C E; Jansen, Anna C; Kelly, Melissa A; Krantz, Ian; Rieubland, Claudine; Ross, Meredith; Rudy, Natasha L; Sanz, Javier; ... (2022). Activating RAC1 variants in the switch II region cause a developmental syndrome and alter neuronal morphology. Brain : a journal of neurology, 145(12), pp. 4232-4245. Oxford University Press 10.1093/brain/awac049

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RAC1 is a highly conserved Rho GTPase critical for many cellular and developmental processes. De novo missense RAC1 variants cause a highly variable neurodevelopmental disorder. Some of these variants have previously been shown to have a dominant negative effect. Most previously reported patients with this disorder have either severe microcephaly or severe macrocephaly. Here, we describe eight patients with pathogenic missense RAC1 variants affecting residues between Q61 and R68 within the switch II region of RAC1. These patients display variable combinations of developmental delay, intellectual disability, brain anomalies such as polymicrogyria and cardiovascular defects with normocephaly or relatively milder micro- or macrocephaly. Pulldown assays, NIH3T3 fibroblast spreading assays and staining for activated PAK1/2/3 and WAVE2 suggest that these variants increase RAC1 activity and over-activate downstream signalling targets. Axons of neurons isolated from Drosophila embryos expressing the most common of the activating variants are significantly shorter, with an increased density of filopodial protrusions. In vivo, these embryos exhibit frequent defects in axonal organization. Class IV dendritic arborization neurons expressing this variant exhibit a significant reduction in the total area of the dendritic arbour, increased branching and failure of self-avoidance. RNAi knock down of the WAVE regulatory complex component Cyfip significantly rescues these morphological defects. These results establish that activating substitutions affecting residues Q61-R68 within the switch II region of RAC1 cause a developmental syndrome. Our findings reveal that these variants cause altered downstream signalling, resulting in abnormal neuronal morphology and reveal the WAVE regulatory complex/Arp2/3 pathway as a possible therapeutic target for activating RAC1 variants. These insights also have the potential to inform the mechanism and therapy for other disorders caused by variants in genes encoding other Rho GTPases, their regulators and downstream effectors.

Item Type:

Journal Article (Original Article)


04 Faculty of Medicine > Department of Gynaecology, Paediatrics and Endocrinology (DFKE) > Clinic of Human Genetics

UniBE Contributor:

Rieubland, Claudine, Sanz, Javier


600 Technology > 610 Medicine & health




Oxford University Press




André Schaller

Date Deposited:

06 Jan 2023 08:22

Last Modified:

06 Jan 2023 23:22

Publisher DOI:


PubMed ID:


Uncontrolled Keywords:

RAC1 WAVE regulatory complex intellectual disability polymicrogyria small GTPases




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