Screening for mercaptopurine intolerance in ALL - target the genes or their product?

To avoid toxicity, patients with inherited intolerance to thiopurines require major dose reductions of six mercaptopurine (6MP) for acute lymphoblastic leukaemia (ALL) maintenance treatment. Germline variants in the NUDT15 gene are emerging as the most common cause of 6MP intolerance in East Asian populations. New approaches are being developed to identify susceptibility to 6MP toxicity in order to appropriately tailor dosing schedules for at-risk patients. Commentary on: Tanaka et al. Prominence of NUDT15 genetic variation associated with 6-mercaptopurine tolerance in a genome-wide association study of Japanese children with acute lymphoblastic leukaemia. Br J Haematol 2022;199:260-269 and Yoshida et al. Low NUDT15 expression levels due to biallelic NUDT15 variants and 6-mercaptopurine intolerance. Br J Haematol 2022;199:270-276.