HLA-DRB1 and Parkinson disease: Furthermore, the allele frequency was significantly higher in patients with an onset age ≤50 than in patients with an onset age >50(0.0678 vs. 0.0342, pc = 0.012, statistic Power >0.75), suggesting that people carrying the HLA-DRB1*0301 allele may have a tendency for an early onset of PD.