HLA-DRB1 and Parkinson disease: In our study, the allele frequency of HLA-DRB1*0406 in PD patients was significantly lower than in healthy controls (0.0013 vs.0.0308, pc = 3.295E-5, statistic Power >0.75) in series 1, but the difference was not achieve statistical significance in series 2 (0.0078 vs. 0.0267, p = 0.097, pc = 1), this inconsistency may be due to a sampling bias.