A pathogenic variant in RAB32 causes autosomal dominant Parkinson's disease and activates LRRK2 kinase.

Background: Parkinson's disease (PD) is a progressive neurodegenerative disorder. Mendelian forms have revealed multiple genes, with a notable emphasis on membrane trafficking; RAB GTPases play an important role in PD as a subset are both regulators and substrates of LRRK2 protein kinase. To explore the role of RAB GTPases in PD, we undertook a comprehensive examination of their genetic variability in familial PD.
Methods: Affected probands from 130 multi-incident PD families underwent whole-exome sequencing and genotyping, Potential pathogenic variants in 61 RAB GTPases were genotyped in relatives to assess disease segregation. These variants were also genotyped in a larger case-control series, totaling 3,078 individuals (2,734 with PD). The single most significant finding was subsequently validated within genetic data (6,043 with PD). Clinical and pathologic findings were summarized for gene-identified patients, and haplotypes were constructed. In parallel, wild-type and mutant RAB GTPase structural variation, protein interactions, and resultant enzyme activities were assessed.
Findings: We found RAB32 c.213C>G (Ser71Arg) to co-segregate with autosomal dominant parkinsonism in three multi-incident families. RAB32 Ser71Arg was also significantly associated with PD in case-control samples: genotyping and database searches identified thirteen more patients with the same variant that was absent in unaffected controls. Notably, RAB32 Ser71Arg heterozygotes share a common haplotype. At autopsy, one patient had sparse neurofibrillary tangle pathology in the midbrain and thalamus, without Lewy body pathology. In transfected cells the RAB32 Arg71 was twice as potent as Ser71 wild type to activate LRRK2 kinase.
Interpretation: Our study provides unequivocal evidence to implicate RAB32 Ser71Arg in PD. Functional analysis demonstrates LRRK2 kinase activation. We provide a mechanistic explanation to expand and unify the etiopathogenesis of monogenic PD.
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: AR receives unrestricted research support from the Dr. Ali Rajput Endowment for Parkinson’s Disease and Movement Disorders; in the past two years AR has received honoraria from CQDM/Brain Canada and Ipsen Biopharmaceuticals Canada. MSG reports grants from NIH/NINDS and the Michael J. Fox Foundation for Parkinson’s Research. AJS has received fees from Neurocrine (Chair, DSMB), AskBio (Member, DSMB) and Capsida (advisor), receives a stipend from the International Parkinsons and Movement Disorders Society (Editor-in-Chief, Movement Disorders) and grant funding from Michael J. Fox Foundation, Weston Brain Institute and Brain Canada. ZGO 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 (CCNA). MJF reports US patents associated with LRRK2 mutations and mouse models (8409809, 8455243), and methods of treating neurodegenerative disease (20110092565). SAC 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, the VGH and UBC Hospital Foundation, Rick’s Heart Foundation and the Jack and Darlene Poole Foundation.