Gustavsson EK, Follett J, Trinh J, Barodia SK, Real R, Liu Z, Grant-Peters M, Fox JD, Appel-Cresswell S, Stoessl AJ, Rajput A, Rajput AH, Auer R, Tilney R, Sturm M, Haack TB, Lesage S, Tesson C, Brice A, Vilariño-Güell C, Ryten M, Goldberg MS, West AB, Hu MT, Morris HR, Sharma M, Gan-Or Z, Samanci B, Lis P, Periñan MT, Amouri R, Ben Sassi S, Hentati F, Tonelli F, Alessi DR, and Farrer MJ
Background: Parkinson's disease is a progressive neurodegenerative disorder with multifactorial causes, among which genetic risk factors play a part. The RAB GTPases are regulators and substrates of LRRK2, and variants in the LRRK2 gene are important risk factors for Parkinson's disease. We aimed to explore genetic variability in RAB GTPases within cases of familial Parkinson's disease., Methods: We did whole-exome sequencing in probands from families in Canada and Tunisia with Parkinson's disease without a genetic cause, who were recruited from the Centre for Applied Neurogenetics (Vancouver, BC, Canada), an international consortium that includes people with Parkinson's disease from 36 sites in 24 countries. 61 RAB GTPases were genetically screened, and candidate variants were genotyped in relatives of the probands to assess disease segregation by linkage analysis. Genotyping was also done to assess variant frequencies in individuals with idiopathic Parkinson's disease and controls, matched for age and sex, who were also from the Centre for Applied Neurogenetics but unrelated to the probands or each other. All participants were aged 18 years or older. The sequencing and genotyping findings were validated by case-control association analyses using bioinformatic data obtained from publicly available clinicogenomic databases (AMP-PD, GP2, and 100 000 Genomes Project) and a private German clinical diagnostic database (University of Tübingen). Clinical and pathological findings were summarised and haplotypes were determined. In-vitro studies were done to investigate protein interactions and enzyme activities., Findings: Between June 1, 2010, and May 31, 2017, 130 probands from Canada and Tunisia (47 [36%] female and 83 [64%] male; mean age 72·7 years [SD 11·7; range 38-96]; 109 White European ancestry, 18 north African, two east Asian, and one Hispanic] underwent whole-exome sequencing. 15 variants in RAB GTPase genes were identified, of which the RAB32 variant c.213C>G (Ser71Arg) cosegregated with autosomal dominant Parkinson's disease in three families (nine affected individuals; non-parametric linkage Z score=1·95; p=0·03). 2604 unrelated individuals with Parkinson's disease and 344 matched controls were additionally genotyped, and five more people originating from five countries (Canada, Italy, Poland, Turkey, and Tunisia) were identified with the RAB32 variant. From the database searches, in which 6043 individuals with Parkinson's disease and 62 549 controls were included, another eight individuals were identified with the RAB32 variant from four countries (Canada, Germany, UK, and USA). Overall, the association of RAB32 c.213C>G (Ser71Arg) with Parkinson's disease was significant (odds ratio [OR] 13·17, 95% CI 2·15-87·23; p=0·0055; I 2 =99·96%). In the people who had the variant, Parkinson's disease presented at age 54·6 years (SD 12·75, range 31-81, n=16), and two-thirds had a family history of parkinsonism. RAB32 Ser71Arg heterozygotes shared a common haplotype, although penetrance was incomplete. Findings in one individual at autopsy showed sparse neurofibrillary tangle pathology in the midbrain and thalamus, without Lewy body pathology. In functional studies, RAB32 Arg71 activated LRRK2 kinase to a level greater than RAB32 Ser71., Interpretation: RAB32 Ser71Arg is a novel genetic risk factor for Parkinson's disease, with reduced penetrance. The variant was found in individuals with Parkinson's disease from multiple ethnic groups, with the same haplotype. In-vitro assays show that RAB32 Arg71 activates LRRK2 kinase, which indicates that genetically distinct causes of familial parkinsonism share the same mechanism. The discovery of RAB32 Ser71Arg also suggests several genetically inherited causes of Parkinson's disease originated to control intracellular immunity. This shared aetiology should be considered in future translational research, while the global epidemiology of RAB32 Ser71Arg needs to be assessed to inform genetic counselling., Funding: National Institutes of Health, the Canada Excellence Research Chairs program, Aligning Science Across Parkinson's, the Michael J Fox Foundation for Parkinson's Research, and the UK Medical Research Council., Competing Interests: Declaration of interests AR receives unrestricted research support from the Dr Ali Rajput Endowment for Parkinson's Disease and Movement Disorders; in the past 2 years AR has received honoraria from Quebec Consortium for Drug Discovery–Brain Canada and Ipsen Biopharmaceuticals Canada. MSG reports grants from National Institutes of Health (NIH)–National Institute of Neurological Disorders and Stroke (NINDS) and the Michael J Fox Foundation for Parkinson's Research. AJS has received fees from Neurocrine (Chair, Data and Safety Monitoring Board [DSMB]), AskBio (Member, DSMB) and Capsida (advisor), receives a stipend from the International Parkinson's and Movement Disorders Society (Editor-in-Chief, Movement Disorders) and grant funding from Michael J Fox Foundation, Weston Brain Institute, and Brain Canada. ZG-O received consultancy fees from Bial Biotec, Bial, Capsida, Handl Therapeutics, Idorsia, Neuron23, Ono Therapeutics, Prevail Therapeutics, UCB, and Vanqua. He reports grants from the Michael J Fox Foundation for Parkinson's Research, The Weston Family Foundation, The Silverstein Foundation, NIH, and the Canadian Consortium on Neurodegeneration in Aging. HRM is employed by University College Londn. In the last 12 months he reports paid consultancy from Roche, Aprinoia, AI Therapeutics, and Amylyx; lecture fees or honoraria from BMJ, Kyowa Kirin, Movement Disorders Society; and research grants from Parkinson's UK, Cure Parkinson's Trust, PSP Association, Medical Research Council, and Michael J Fox Foundation. HRM is a co-applicant on a patent application related to C9ORF72: method for diagnosing a neurodegenerative disease (PCT/GB2012/052140). MJF reports US patents associated with LRRK2 mutations and mouse models (8409809 and 8455243), and methods of treating neurodegenerative disease (20110092565). SA-C has received honoraria from Merz, and grant funding from the Pacific Parkinson's Research Institute, the Weston Family Foundation, Parkinson Canada, Canadian Institutes of Health Research (CIHR), the VGH and UBC Hospital Foundation, Rick's Heart Foundation, and the Jack and Darlene Poole Foundation. All other authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license. Published by Elsevier Ltd.. All rights reserved.)