Recently, common variant in NUDT15 (i.e., rs116855232) was identified to largely explain thiopurine-induced leukopenia in ALL and immune diseases (e.g., inflammatory bowel disease) in East Asians (Yang et al., 2014; Yang et al., 2015; Moriyama et al., 2016). Here, NUDT15 is linked to Decreased total leukocyte count.