Three types of arginine methylation exist in mammalian cells: monomethylarginine (MMA), asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA). Type I PRMTs ((CARM1, PRMT1, PRMT2, PRMT3, PRMT6, and PRMT8) catalyze ADMA, while type II PRMTs (e.g. PRMTs 5 and 7) catalyze SDMA. Type II PRMTs are found to be strongly implicated in diseases like cancer. For example, PRMT5 plays a role in the repression of certain tumor suppressor genes such as RB tumor suppressors while PRMT7 overexpression is observed in breast cancer