CDKN2A and neurodegenerative disease: Bmi-1, a PcG epigenetic regulator that blocks expression of the p16Ink4a CDK inhibitor, plays a key role in aging, and dysregulation of the Bmi-1/p16Ink4a pathway is believed to cause failure of adult stem cell homeostasis and the onset of aging-associated degenerative diseases (Dhawan et al., 2009; Sousa-Victor et al., 2014).