To establish whether the presence of variants in the TPMT and NUDT15 genes was associated with diseases phenotypes, we analyzed the association of genotypes with age at diagnosis, gender, risk factors (smoking, appendicitis, tonsillectomy, and family history of IBDs), disease location, disease behavior, the presence of non-perianal fistulas and perianal disease, the presence of extra-intestinal manifestations, and surgical resection. The gene discussed is NUDT15; the disease is appendicitis.