Because white blood cell count-based dose adjustments are regularly performed for known NUDT15- deficient patients and result in a reduced risk of neutropenia and febrile neutropenia26, the accurate determination of patients with NUDT15*3/*6 may avoid them from receiving a high dose of mercaptopurine; even if the mercaptopurine dose was already reduced based on the results of NUDT15*1/*2 genetic analysis. The gene discussed is NUDT15; the disease is neutropenia.