Furthermore, when restricting our analyses to participants from the old age group, i.e., those closer to a potential onset of PD, higher genetic PD risk was associated with increased proportions of myeloid dendritic cells (∆R2 = 2.5%, p = 0.019) and CD27+ CD4+ memory T cells (∆R2 = 1.6%, p = 0.043). This evidence concerns the gene CD4 and Parkinson disease.