Notably, a study in patients with Ashkenazi Jewish heritage showed an increased risk for PD in both patients with GD (carrying 2 mutant GBA1 alleles) and heterozygote carriers (carrying 1 mutant GBA1 allele); however, the overall risk for developing the disease was similar between the two groups of patients, suggesting that the number of mutant alleles may not affect the penetrance [43]. This evidence concerns the gene GBA1 and Parkinson disease.