We conducted a meta analysis of Parkinson’s disease genome-wide association studies using a common set of 7,893,274 variants across 13,708 cases and 95,282 controls. Twenty-six loci were identified as genome-wide significant; these and six additional previously reported loci were then tested in an independent set of 5,353 cases and 5,551 controls. Of the 32 tested SNPs, 24 replicated, including 6 novel loci. Conditional analyses within loci show four loci including GBA, GAK/DGKQ, SNCA, and HLA contain a secondary independent risk variant. In total we identified and replicated 28 independent risk variants for Parkinson disease across 24 loci. While the effect of each individual locus is small, a risk profile analysis revealed a substantial cummulative risk in a comparison highest versus lowest quintiles of genetic risk (OR=3.31, 95% CI: 2.55, 4.30; p-value = 2×10−16). We also show 6 risk loci associated with proximal gene expression or DNA methylation.

Our objective was to design a genotyping platform that would allow rapid genetic characterization of samples in the context of genetic mutations and risk factors associated with common neurodegenerative diseases. The platform needed to be relatively affordable, rapid to deploy, and use a common and accessible technology. Central to this project, we wanted to make the content of the platform open to any investigator without restriction. In designing this array we prioritised a number of types of genetic variability for inclusion, such as known risk alleles, disease causing mutations, putative risk alleles, and other functionally important variants. The array was primarily designed to allow rapid screening of samples for disease causing mutations, and large population studies of risk factors. Notably, an explicit aim was to make this array widely available to facilitate data sharing across and within diseases. The resulting array, NeuroX, is a remarkably cost and time effective solution for high quality genotyping. NeuroX comprises a backbone of standard Illumina exome content of approximately 240,000 variants, and over 24,000 custom content variants focusing on neurological diseases. Data is generated at ~$50–$60 per sample using a 12-sample format chip and regular Infinium infrastructure; thus genotyping is rapid, and accessible to many investigators. Here, we describe the design of NeuroX, discuss the utility of NeuroX in the analyses of rare and common risk variants, and present quality control metrics and a brief primer for the analysis of NeuroX derived data.

Several genes and risk factors are associated with Parkinson’s disease (PD). Although many of the genetic markers belong to a common pathway, a unifying pathogenetic mechanism is yet to be found. Also, missing heritability analyses have estimated that only part of the genetic influence contributing to PD has been found. Here, we carried out whole-exome sequencing (WES) on 438 Finnish patients with early-onset PD. We also re-analyzed previous data from genome-wide association studies (GWAS) on the same cohort. Variants in the CEL gene/locus were associated with PD in both GWAS and WES analysis. Exome-wide gene-based association tests also identified the MPHOSPH10, TAS2R19 and SERPINA1 genes in the discovery dataset (p<2.5E-6). MPHOSPH10 had estimated odds ratio (OR) of 1.53 and the rs141620200 variant in SERPINA1 had OR of 1.27. We identified several candidate genes, but further investigation is required in order to determine the role of these genes in PD.

IMPORTANCE Pathogenic variants in LRRK2 are a relatively common genetic cause of Parkinson disease (PD). Currently, the molecular mechanism underlying disease is unknown, and gain and loss of function (LOF) models of pathogenesis have been postulated. LRRK2 variants are reported to result in enhanced phosphorylation of substrates and increased cell death. However, the double knockout of Lrrk2 and its homologue Lrrk1 results in neurodegeneration in a mouse model, suggesting that disease may occur by LOF. Because LRRK2 inhibitors are currently in development as potential disease-modifying treatments in PD, it is critical to determine whether LOF variants in LRRK2 increase or decrease the risk of PD. OBJECTIVE To determine whether LRRK1 and LRRK2 LOF variants contribute to the risk of developing PD. DESIGN, SETTING, AND PARTICIPANTS To determine the prevailing mechanism of LRRK2-mediated disease in human populations, next-generation sequencing data from a large case-control cohort (>23 000 individuals) was analyzed for LOF variants in LRRK1 and LRRK2. Data were generated at 5 different sites and 5 different data sets, including cases with clinically diagnosed PD and neurologically normal control individuals. Data were collected from 2012 through 2017. MAIN OUTCOMES AND MEASURES Frequencies of LRRK1 and LRRK2 LOF variants present in the general population and compared between cases and controls. RESULTS Among 11 095 cases with PD and 12 615 controls, LRRK1 LOF variants were identified in 0.205% of cases and 0.139% of controls (odds ratio, 1.48; SE, 0.571; 95% CI, 0.45-4.44; P = .49) and LRRK2 LOF variants were found in 0.117% of cases and 0.087% of controls (odds ratio, 1.48; SE, 0.431; 95% CI, 0.63-3.50; P = .36). All association tests suggested lack of association between LRRK1 or LRRK2 variants and PD. Further analysis of lymphoblastoid cell lines from several heterozygous LOF variant carriers found that, as expected, LRRK2 protein levels are reduced by approximately half compared with wild-type alleles. CONCLUSIONS AND RELEVANCE Together these findings indicate that haploinsufficiency of LRRK1 or LRRK2 is neither a cause of nor protective against PD. Furthermore, these results suggest that kinase inhibition or allele-specific targeting of mutant LRRK2 remain viable therapeutic strategies in PD.