Xenobiotic and folate metabolic pathways are important for the maintenance of genetic stability and may influence susceptibility to the development of childhood acute lymphoblastic leukaemia (ALL). In this study, we investigated 10 polymorphisms in 6 genes (GSTM1-present/null, GSTT1-present/null, GSTP1 1578A > G, NQO1 609C > T, MTHFR 677C > T, MTHFR 1298A > C, MTHFD1 1958G > A, 3'-TYMS 1494 6bp-deletion/insertion, 5'-TYMS 28bp-tandem repeats, and SLC19A1 80G > A) in a cohort of 185 Javanese children with ALL and 177 healthy controls. In ALL patients, none of the polymorphisms demonstrated a statistically significant association with ALL after correcting for multiple comparisons. Gender-stratified analysis showed that in girls, GSTT1-null genotype was associated with increased ALL risk (OR = 2.20; p = 0.027), while GSTP1 1578AG genotype was associated with reduced risk (OR = 0.43; p = 0.031). Strong linkage disequilibrium between the MTHFR 677C > T and 1298A > C polymorphisms was observed (D' = 1.0; r(2) = 0.072). The haplotypes 677C-1298C and 677T-1298A were associated with a reduced risk of ALL (OR = 0.68 and 0.64, respectively; gender-adjusted global p = 0.028). Classification and regression tree (CART) analysis was employed to identify potential high-order gene-gene interactions and cluster subjects into susceptibility groups. SLC19A1 80G > A emerged as the predominant polymorphism associated with risk of ALL. Individuals simultaneously carrying MTHFR 1298AA, 3'-TYMS 6bp deletion(s) and SLC19A1 80A-allele(s) were at higher disease risk (OR = 2.21; p < 0.001). On the contrary, simultaneous possession of MTHFR 1298CC, 3'-TYMS 6bp homozygosity and SLC19A1 80A-allele(s) conferred lower risk (OR = 0.25; p = 0.004). Carriage of NQO1 609C-allele amongst SLC19A1 80GG genotype was associated with lower risk (OR = 0.47; p = 0.003). In conclusion, our study has demonstrated the importance of gender and gene-gene interaction within the xenobiotic and folate pathways in modulating childhood ALL susceptibility.

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