Biallelic variants in ARHGAP19 cause a motor-predominant neuropathy with asymmetry and conduction slowing

Charcot-Marie-Tooth Disease is a clinically and genetically heterogeneous group of hereditary neuropathies, with over 100 causative genes identified to date. Despite progress in genetic sequencing, around a quarter of patients remain unsolved. Through international collaborations, we identified 16 recessive variants in Rho GTPase activating protein 19 (ARHGAP19) causing motor-predominant neuropathy with conduction slowing in 25 individuals from 20 unrelated multi-ancestry families. ARHGAP19 is a GTPase-activating protein with activity towards RhoA. In vitro biochemical assays revealed that variants located within the GAP domain cause loss of GAP activity. iPSc-derived motor neurons exhibited 50% knockdown of ARHGAP19 protein. In vivo genetic perturbations of the Drosophila melanogaster ARHGAP19 ortholog RhoGAP54D reduced self-driven locomotor activity and startle responses to visual stimuli. Zebrafish loss-of-function models similarly exhibited movement deficits, coupled with increased motor neuron axonal branching but shorter caudal primary motor neurons. Together, these findings establish ARHGAP19 as a novel cause of early-onset neuropathy through a loss-of-function mechanism. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement We thank the patient and relatives for consent to be part of the study as well as the clinicians for helping with patient phenotyping. The families were collected as part of the SYNaPS Study Group collaboration funded by The Wellcome Trust and strategic award (Synaptopathies) funding (WT093205 MA and WT104033AIA) and research was conducted as part of the Queen Square Genomics group at University College London, supported by the National Institute for Health Research University College London Hospitals Biomedical Research Centre. This work was partly supported by an MRC strategic award to establish an International Centre for Genomic Medicine in Neuromuscular Diseases (ICGNMD) MR/S005021/1 and ND, SE, CR, PT, MGH, MMR and HH received direct support from this award. JP is supported by Medical Research Future Fund (MRFF) Genomics Health Futures Mission (APP2007681) and by the Australian Government Research Training Program. LVdV is supported by a predoctoral fellowship of the Research Fund - Flanders (FWO) under grant agreement N11F0921N. TS is member of the European Reference Network for Rare Neuromuscular Diseases (ERN EURO-NMD). JB is supported by a Senior Clinical Researcher mandate of the Research Fund - Flanders (FWO) under grant agreement N1805021N. ANB gratefully acknowledges the support of SVIKV and the use of the services and facilities of the Koc University Research Center for Translational Medicine (KUTTAM), funded by the Presidency of Turkey, Head of Strategy and Budget. We thank collaborator Simon Bullock (University of Cambridge) for plasmids, and Florencia di Pietro for characterization of the RhoGAP54D loss of function allele. JECJ was funded by an MRC Senior Non-Clinical Fellowship (MR/V03118X/1). Work in the Bellaiche group is funded by the CNRS, the INSERM and the Institut Curie as well as by the ANR (TiMecaDiv 20CE13000801) grant. TBH was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation 418081722, 433158657), and the European Commission (Recon4IMD GAP101080997). This work was supported in part by the Fund for Scientific Research (FWO Flanders) (research grants G048220N and G0A2122N to A.J.), the Research Fund of the University of Antwerp (doctoral grant to C.A.), the Association Belge contre les Maladies Neuromusculaires (ABMM-Telethon) (research grants to A.J.), the French Muscular Dystrophy Association (AFM-Telethon, research grant 23708 to A.J.). JPark was supported by the Clinician Scientist program PRECISE.net funded by the Else Kroner-Fresenius-Stiftung. Work in the Lamarche-Vane group funded by Natural Sciences and Engineering Research Council of Canada grant RGPIN/04809 2017 and CIHR project grant PJT 180367. Leif Leclaire holds a CIHR master studentship. RH is supported by the Wellcome Discovery Award (226653/Z/22/Z), the Medical Research Council (UK) (MR/V009346/1), the Addenbrookes Charitable Trust (G100142), the Evelyn Trust, the Stoneygate Trust, the Lily Foundation, Ataxia UK, Action for AT, the Muscular Dystrophy UK. This research was supported by the NIHR Cambridge Biomedical Research Centre (BRC 1215 20014). The views expressed are those of the authors and not necessarily those of the NIHR or the Department of Health and Social Care. We are also grateful to Queen Square Genomics at the Institute of Neurology University College London, supported by the National Institute for Health Research University College London Hospitals Biomedical Research Centre, for the bioinformatics support. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Individuals and/or their legal guardians recruited for this study gave informed consent for their participation. This study received approval from the Review Boards and Bioethics Committees at University College London Hospital (project 06/N076). Permission for inclusion of their anonymized medical data in this cohort, including photographs, was obtained using standard forms at each local site by the responsible referring physicians. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors [https://databases.lovd.nl/shared/variants/ARHGAP19?search\_var\_status=%3D%22Marked%22%7C%3D%22Public%22][1] [1]: https://databases.lovd.nl/shared/variants/ARHGAP19?search_var_status=%3D%22Marked%22%7C%3D%22Public%22