Parkinson disease (PD) is the second most common neurodegenerative condition worldwide, characterized by bradykinesia, rigidity, and tremor.1 Genome-wide association studies (GWASs) have discovered more than 40 loci significantly associated with PD risk.2 However, these studies are limited to narrowing PD risk down to a genomic region encompassing several candidate genes. The causal genes underlying each locus, as well as the mechanism by which they confer PD risk, often remain unclear. These issues can be resolved by complementing GWAS data with quantitative trait loci (QTL) data sets, which describe associations of an individual’s genotype with gene expression (eQTLs), splicing or methylation. For example, such efforts applied to the 7p15.3 locus have shown that PD risk variants regulate GPNMB (OMIM 604368) expression.3 Improvements to the understanding of the genes and mechanisms via which GWAS risk variants act may be instrumental to our understanding of the pathogenesis of PD.
