GBA1 and Lewy body dementia: Case–control genome-wide association studies (GWAS) in the past decade have identified 90 common variant risk loci associated with Parkinson’s disease10 and 5 risk loci associated with dementia with Lewy bodies.11 Variation in several genes, including GBA1, TMEM175 and SNCA, confers risk for both diseases, suggesting overlapping pathogenesis and underlying biological dysfunction.