HLA-DRB1 and Parkinson disease: We found that the allele frequencies of HLA-DRB1*0301 were higher in both PD subgroups (onset age ≤50 and onset age >50) than in their healthy control subgroups (0.0678 vs. 0.0263, p = 0.001, 0.0342 vs. 0.0213, p = 0.008, respectively), these differences were only occurred in male subgroups (0.0892 vs. 0.0286, p = 0.001, 0.0412 vs. 0.0230, p = 0.014, respectively).