NUDT15*18 is assigned no function based on limited evidence. One patient identified with the genotype NUDT15*1/*18 received 50 mg of 6-MP daily and experienced pancytopenia after 3 months of treatment. However, this patient was also heterozygous for an inactivating TPMT allele (30728528). NUDT15*18 is characterized by c.221delA, causing a frameshift (p.N74fs), that is predicted to impair protein function by CADD and PhD-SNP6. The deletion occurs in exon 2, which is within the Nudix hydrolase domain, and NUDT15*18 is predicted to produce a protein targeted for nonsense-mediated decay.