Submitted September 4, 2007
Accepted December 15, 2007
DNA variants in dihydrofolate reductase gene and outcome in childhood ALL
Stephanie Dulucq, Genevieve St-Onge, Vincent Gagne, Marc Ansari, Daniel Sinnett, Damian Labuda, Albert Moghrabi, and Maja Krajinovic*
Research Center, CHU Sainte-Justine, Montreal, Quebec, Canada
Department of Pediatrics, University of Montreal, Montreal, Quebec, Canada
Department of Pharmacology, University of Montreal, Montreal, Quebec, Canada
* Corresponding author; email: maja.krajinovic{at}umontreal.ca.
Dihydrofolate reductase (DHFR) is the major target of methotrexate (MTX), a key component in childhood acute lymphoblastic leukemia (ALL) treatment. Fifteen polymorphisms in DHFR promoter were analyzed and three sites (C-1610G/T; C-680A; A-317G) were identified as sufficient to define observed haplotypes (tagSNPs). These polymorphisms were investigated for association with treatment response in 277 children with ALL. Lower EFS was associated with homozygosity for the allele A -317 and C -1610 (p =0.03 and 0.02), and with the haplotype *1, defined by both C -1610 and A -317 alleles (p = 0.03). The haplotype *1 conferred higher transcriptional activity (p<0.01, compared to haplotypes generating minimal luciferase expression). Quantitative mRNA analysis showed higher DHFR levels for particular haplotype *1 carriers (p= p<0.01). The analysis combining haplotype *1 with thymidylate synthase (TS) and cyclin D1 (CCND1) genotypes previously shown to affect ALL outcome, showed that the number of event-predisposing genotypes was associated with increasingly lower EFS (p<0.0005). In conclusion, DHFR promoter polymorphisms are associated with worse ALL outcome, likely due to a higher DHFR expression. Combined effect among genes of the folate cycle can further accentuate differences in the response to the treatment.
