NUDIX hydrolase 15 (NUDT15) is an enzyme directly involved in the metabolism of thiopurines, a class of immunosuppressive drugs, as it catalyses the conversion of active metabolites into less toxic metabolites. Thiopurines are the mainstay in the treatment of several forms of cancer, immune system disorders and the prevention of rejection after organ transplantation. Individuals with reduced or absent NUDT15 activity have a higher sensitivity to thiopurines at standard doses and are at a higher risk of toxic side effects. 
Genetic variations in the TPMT and NUDT15 genes strongly influence the safety of thiopurine therapy. The genotyping of NUDT15 is therefore complementary to the identification of the TPMT risk allele: the latter is the main genetic cause of thiopurine intolerance in Europeans and Africans, while NUDT15 deficiency is most common among East Asians (22.6%), followed by South Asians (13.6%) and Native American populations (12.5%-21.2%)

NUDT15*3
Also referred to as rs116855232 or 415C>T

NUDT15*6
Also referred to as rs746071566  or 55_56insGAGTCG ; V18_V19insGV (old : rs869320766)

NUDT15*9
Also referred to as rs746071566  or 37_42delGGAGTC ; G17_V18del