In PD, the most significant association was observed for HLA-DQA1*03:01 (OR = 0.89[0.87; 0.91]; P = 2.3E-20), which was the second most significant allele in AD (OR = 0.89[0.87; 0.91]; P = 1.7E-18). This evidence concerns the gene HLA-DQA1 and Alzheimer disease.