One study marked an observed increase in the proportional CD4 + and CD3 + T cells as well as the CD4 + /CD8 + ratio in PD patients [52]; whereas, another study showed a decrease in the CD3 + , CD8 + T cells and B lymphocyte subsets in addition to a decrease in CD4 + T cells [114, 229]. This evidence concerns the gene CD8A and Parkinson disease.