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. Here, TPMT is linked to autoimmune disease.