Surmounting evidence supports the influence of NUDT15 variation on the development of toxicity in individuals of European ancestry, including TIM in patients with IBD who have been exposed to AZA and 6-MP.23,44 Additionally, the combination of loss-of-function alleles in both TPMT and NUDT15 has been associated with an increased probability of developing adverse reactions to thiopurines.23 Thus, there is a growing body of evidence supporting the merit of testing NUDT15 in individuals of European ancestry, in addition to Asian and Admixed American ancestry. This evidence concerns the gene NUDT15 and inflammatory bowel disease.