CDKN1A and gonorrhea: The TSG genes reviewed can be classified according to the degree of methylation: Frequently methylated genes (i.e. CDKN2A, GADD45y, FGFR2, caspase-8, and PTAG) demonstrate methylation in over 50% of PAs; moderately methylated genes (i.e. TSP-1, RASSF1A, Rb1, p73, MGMT, and E-cadherin) demonstrate methylation in 20-50% of PAs; and infrequently methylated genes (i.e. p14, DAP kinase, TIMP3, p21, and p27) are methylated in <20% of PAs [39,40,58–60,67,68,70].