Furthermore, Kouli et al. [94] assessed immunosenescence in CD8+ T cells in PD patients vs controls by testing several aging markers such as telomere length, the expression levels of the telomerase reverse transcriptase enzyme (TERT) and of cyclin dependent kinase inhibitors (p16INK4a and p21CIP1/Waf1). Here, CDKN1A is linked to Parkinson disease.