NUDT15 and inflammatory bowel disease: Background/Objectives: Thiopurines remain a cornerstone in the management of inflammatory bowel disease (IBD) and gastrointestinal immune diseases but are associated with significant interindividual variability in efficacy and toxicity, mainly influenced by polymorphisms in Thiopurine S-methyltransferase TPMT and Nudix Hydrolase 15 NUDT15. This study aimed to assess the frequency of TPMT and NUDT15 variants in a pediatric cohort and evaluate their clinical impact to support a pharmacogenetic-guided approach to thiopurine therapy.