Evaluation of the synapse adhesion molecule Kirrel3 in neurological disease

The synaptic adhesion molecule KIRREL3 regulates synapse development in mice and is implicated in human neurological disorders, including autism spectrum disorder, intellectual disability, and Jacobsen syndrome (chromosome 11q deletion syndrome). However, its status as a definitive human disease gene remains unresolved, likely due to the rarity of KIRREL3-related disorders and significant gaps in understanding its molecular mechanisms. Current knowledge is further fragmented across disparate clinical and basic research reports, often buried in supplemental data. This review synthesizes existing evidence to enable clinicians and scientists to better evaluate KIRREL3 variants as potentially disease causing. We review its conserved role in mediating neuron-to-neuron interactions during axon targeting and synapse formation in mice and how disruptions to these interactions could contribute to neurological pathology in humans. We also discuss how disease-associated variants alter KIRREL3 function. Our analysis underscores the need for integrated studies spanning basic and clinical investigation to validate KIRREL3’s disease association and advance future interventions for KIRREL3-related disorders

The p190 RhoGAPs, ARHGAP35, and ARHGAP5 are implicated in GnRH neuronal development: Evidence from patients with idiopathic hypogonadotropic hypogonadism, zebrafish, and in vitro GAP activity assay

International audiencePurpose: The study aimed to identify novel genes for idiopathic hypogonadotropic hypogonadism (IHH).Methods: A cohort of 1387 probands with IHH underwent exome sequencing and de novo, familial, and cohort-wide investigations. Functional studies were performed on 2 p190 Rho GTPase-activating proteins (p190 RhoGAP), ARHGAP35 and ARHGAP5, which involved in vivo modeling in larval zebrafish and an in vitro p190A-GAP activity assay.Results: Rare protein-truncating variants (PTVs; n = 5) and missense variants in the RhoGAP domain (n = 7) in ARHGAP35 were identified in IHH cases (rare variant enrichment: PTV [unadjusted P = 3.1E-06] and missense [adjusted P = 4.9E-03] vs controls). Zebrafish modeling using gnrh3:egfp phenotype assessment showed that mutant larvae with deficient arhgap35a, the predominant ARHGAP35 paralog in the zebrafish brain, display decreased GnRH3-GFP+ neuronal area, a readout for IHH. In vitro GAP activity studies showed that 1 rare missense variant [ARHGAP35 p.(Arg1284Trp)] had decreased GAP activity. Rare PTVs (n = 2) also were discovered in ARHGAP5, a paralog of ARHGAP35; however, arhgap5 zebrafish mutants did not display significant GnRH3-GFP+ abnormalities.Conclusion: This study identified ARHGAP35 as a new autosomal dominant genetic driver for IHH and ARHGAP5 as a candidate gene for IHH. These observations suggest a novel role for the p190 RhoGAP proteins in GnRH neuronal development and integrity