Caucasians, Africans, African-Americans, and Asians and

Mercaptopurine (6-MP) is a highly effective chemo-therapeutic agent for the treatment of childhood acute lymphoblastic leukemia (ALL), and is extensively used in therapeutic protocols worldwide [1]. Hematological and hepatic toxicities are the most common adverse effects associated with cumulative toxic plasma con-centrations of 6-MP metabolites [2,3]. Pharmamacoge-netics has provided a molecular approach to guide the individualization of cancer chemotherapy, reducing toxicity and increasing safety of the therapy [4]. Phar-macogenetic studies in childhood ALL have associated toxicity to 6-MP to single nucleotide polymorphism (SNP) in genes coding for 6-MP metabolizing enzymes such as thiopurine S-methyltransferase (TPMT) and inosine triphosphate pyrophosphatase (ITPA) [5,6]. TPMT is a cytosolic enzyme that catalyses the methyla-tion of aromatic and heterocyclic sufohydroxyl groups in 6-MP and their nucleotide metabolites [7]. TPMT exhibits genetic polymorphism in all large ethnic groups, includin