Based on the racial difference in nucleoside diphosphate-linked moiety X-type motif 15 (NUDT15) and thiopurine methyltransferase activity between Caucasians and Asian patients, monitoring their 6-thioguanine nucleotide (6TGN) levels is required to determine the optimal AZA dose for controlling AIP, which is also relevant in other autoimmune diseases. This evidence concerns the gene NUDT15 and autoimmune disease.