HLA-DRB1 and Parkinson disease: Our results revealed that the HLA-DRB1*04 alleles were significant statistically at the ‘possible’ level (uncorrected Fisher’s exact test, p<0.05) with HLA-DRB1*04:02 and -DRB1*04:04 protective in PD and PPMI (Table 3), whereas HLA-DRB1*04:01 was a possible risk allele in the Prodrome and SWEDD groups, and the PPMI cohort (Table 5).