HLA-DRB1 and Parkinson disease: Using unconditional logistic regression analysis adjusted for the age of onset and gender, we found that the HLA-DRB1*0301 allele was positively associated with the risk of PD (OR = 1.963, p = 0.001 in series 1, OR = 2.135, p = 0.019 in series 2, OR = 2.048, p = 3.952E-5 in combined series 1 and series 2), while the HLA-DRB1*0406 allele might be negatively associated with the risk of PD (OR = 0.043, p = 0.002 in series 1, OR = 0.312, p = 0.077 in series 2, OR = 0.118, p = 5.002E-5 in combined series 1 and series 2).