Flow analysis revealed a trend toward reduced total CD8 + T cells in subjects with GG genotype (p = 0.0514; Fig. 8E), while evaluation of CD8+ subsets showed a significant SNP effect in CD8+ central memory cells, decreased CD8+ naïve cells in PD AA participants relative to health control AA participants, and increased CD8+ effector T cells in PD AA relative to healthy control AA participants (Fig. 8F–I). The gene discussed is CD8A; the disease is Parkinson disease.