Homozygous mutations in the GBA gene cause Gaucher disease (GD); through astute clinical observation, it was noted that some GD patients showed parkinsonian features [74], and that heterozygous carriers of these variants had a higher prevalence of PD [75], leading to the discovery that heterozygous variants in GBA can predispose to PD, with an odds ratio (OR) of 5.43 (95% CI, 3.89–7.57) [76]. This evidence concerns the gene GBA1 and Gaucher disease.