Recently, folate metabolic variants including thymidylate synthetase (TYMS) and dihydrofolate reductase (DHFR) were shown to be potential biomarkers of 6-MP-induced myelotoxicity, which could be employed for the individualization of 6-MP therapy when childhood ALL treatment reaches its maintenance phase (Milosevic et al., 2019). Here, DHFR is linked to acute lymphoblastic leukemia.