UCHL1 and Parkinson disease: Using subjects with the CC or CA genotype of UCHL1  S18Y SNP and the CC or CT genotype of SNCA SNP rs356220 as a reference group, those with the AA genotype of UCHL1  S18Y SNP and the TT genotype of SNCA SNP rs356220 had a significantly increased risk of sporadic PD; however, neither multiplicative nor additive interaction was statistically significant (Table 3).