CDKN2A and Parkinson disease: The expression of the cyclin-dependent kinase inhibitor 2A (CDKN2A) gene is positively correlated with cellular senescence and has emerged as a valuable marker of both cellular senescence [59] and the pathogenesis of Parkinson’s disease, since CDKN2A is essential for regulating the cell cycle and providing protection to dopaminergic neurons in the midbrain, which are severely affected in PD.