Background: The frequency of the multi-drug resistance 1 (MDR1) gene C3435T polymorphism differs in various ethnical populations such as Asian, African, and Caucasians populations. A silent C3435T polymorphism in exon 26 of MDR1 has been reported to be associated with a decreased expression of P-gp in TT genotypes carriers compared with CC genotypes carriers.

Materials and Methods: To evaluate the association between MDR1 gene C3435T polymorphism and acute lymphocyte leukemia (ALL), 126 ALL patients (72 males and 54 females) with a mean age of 11.42 ± 6.55 and 139 healthy controls (79 males and 60 females) with a mean age of 12.15 ± 7.5 who were referred to Dr. Sheykh hospital, Mashhad, Iran, between 2005-2007 were enrolled in our study and their C3435T MDR1 polymorphism was investigated using PCR-RFLP.

Results: The mutant homozygous TT and TC genotypes were found to be associated with the incidence of ALL (p<0.05). There was no significant difference for T allele frequency between ALL patients and healthy controls (OR=1.08, 95% CI 0.84-1.66, p=0.33).

Conclusion: TT genotypes carriers are at higher risk of developing ALL than carriers of other genotypes.