CDKN1A and chronic kidney disease: Known alterations at the genetic level tend to occur near genes that regulate the G1/S transition [451], including CKD inhibitors, such as p15 (INK4A), p16 (INK4B), p18 (INK4C), p19 (INK4D), p21 (WAF1), p27 (KIP1), and p57 (KIP2), as well as p53 and Rb [451].