A significant association signal at chromosome 13 was observed in the results of GWAS for thiopurine-induced leukopenia and alopecia; the top hit SNP was rs116855232, NUDT15 Arg139Cys (Supplementary Table 5, Fig. 3a, c, Supplementary Figs. S2, S3a). Here, NUDT15 is linked to Decreased total leukocyte count.