Mutations in the glucocerebrosidase gene, GBA1 (OMIM 606463), cause the autosomal recessive lysosomal storage disorder, Gaucher disease.1 These mutations are the most important genetic risk factor for Parkinson disease (PD),2 exhibiting penetrance of 10% to 30%.3,4 They are present in 5% to 15% of Caucasian patients with PD, 25% of Ashkenazi Jewish patients with PD, and 1% of individuals without PD.5 This evidence concerns the gene GBA1 and Parkinson disease.