With respect to COMT, this gene translates catechol-O-methyltransferase, an enzyme involved in the metabolic degradation of catecholamines, which normally exhibit low activity in leukocytes [89]; in pediatric ALL patients, the COMT-“rs4680” polymorphism was associated with mercaptopurine-induced hepatotoxicity [90]. Here, COMT is linked to acute lymphoblastic leukemia.