NUDT15 and Decreased total leukocyte count: This study identified that the NUDT15 c.415C>T (p.R139C) variant was strongly associated with thiopurine-induced early leukopenia (white blood cell [WBC] count <3000/mm3) (odds ratio [OR] = 35.6; P [combined] = 4.88 × 10−94) [8].