Genetic variants of NHEJ DNA ligase IV can affect the risk of developing multiple myeloma, a tumour characterised by aberrant class switch recombination.

The DNA double stranded break (DSB) repair mechanism, non-homologous end joining (NHEJ) represents an essential step in antigen receptor gene rearrangement mechanisms, processes believed to be intimately involved in the aetiology of lymphoproliferative disease. We investigated the potential impact that previously undescribed polymorphisms identified within NHEJ DNA ligase IV (LIG4) have upon predisposition to several lymphoproliferative disorders, including leukaemia, lymphoma, and multiple myeloma. Two LIG4 polymorphisms were examined, both C>T transitions, which result in the amino acid substitutions A3V and T9I. Inheritance of the LIG4 A3V CT genotype was found to be significantly associated with a two-fold reduction in risk of developing multiple myeloma (OR 0.49, 95% CI 0.27 to 0.89). Similarly, inheritance of the LIG4 T9I CT and the T9I TT genotypes were found to associate with a 1.5-fold reduction (OR 0.77, 95% CI 0.51 to 1.17) and a four-fold reduction (OR 0.22, 95% CI 0.07 to 0.70) in risk of developing multiple myeloma respectively, suggesting a gene dosage effect for this polymorphism. The LIG4 A3V and T9I variant alleles are in linkage disequilibrium (D'=0.95, p<0.0001), and the protective effect associated with these polymorphisms was found to be the result of inheritance of the A3V-T9I CT and A3V-T9I TT haplotypes. These data suggest that genetic variants of NHEJ LIG4 may modulate predisposition to multiple myeloma, a tumour characterised by aberrant immunoglobulin (Ig) class switch recombination.

Polymorphism in glutathione S-transferase P1 is associated with susceptibility to chemotherapy-induced leukemia.

Glutathione S-transferases (GSTs) detoxify potentially mutagenic and toxic DNA-reactive electrophiles, including metabolites of several chemotherapeutic agents, some of which are suspected human carcinogens. Functional polymorphisms exist in at least three genes that encode GSTs, including GSTM1, GSTT1, and GSTP1. We hypothesize, therefore, that polymorphisms in genes that encode GSTs alter susceptibility to chemotherapy-induced carcinogenesis, specifically to therapy-related acute myeloid leukemia (t-AML), a devastating complication of long-term cancer survival. Elucidation of genetic determinants may help to identify individuals at increased risk of developing t-AML. To this end, we have examined 89 cases of t-AML, 420 cases of de novo AML, and 1,022 controls for polymorphisms in GSTM1, GSTT1, and GSTP1. Gene deletion of GSTM1 or GSTT1 was not specifically associated with susceptibility to t-AML. Individuals with at least one GSTP1 codon 105 Val allele were significantly over-represented in t-AML cases compared with de novo AML cases [odds ratio (OR), 1.81; 95% confidence interval (CI), 1.11-2.94]. Moreover, relative to de novo AML, the GSTP1 codon 105 Val allele occurred more often among t-AML patients with prior exposure to chemotherapy (OR, 2.66; 95% CI, 1.39-5.09), particularly among those with prior exposure to known GSTP1 substrates (OR, 4.34; 95% CI, 1.43-13.20), and not among those t-AML patients with prior exposure to radiotherapy alone (OR,1.01; 95% CI, 0.50-2.07). These data suggest that inheritance of at least one Val allele at GSTP1 codon 105 confers a significantly increased risk of developing t-AML after cytotoxic chemotherapy, but not after radiotherapy.

Poor metabolizers at the cytochrome P450 2D6 and 2C19 loci are at increased risk of developing adult acute leukaemia.

We have genotyped over 550 cases of acute leukaemia and 950 matched controls from a population-based case-control study, to investigate the impact cytochrome P450s 2D6, 2C19 and 1A1 have on susceptibility to adult acute leukaemia. Analysis included potential associations between polymorphic status and acute myeloid leukaemia (AML), acute lymphoblastic leukaemia (ALL), plus the FAB and cytogenetic subtypes therein. A significant increased risk was found for CYP2D6 poor metabolizer phenotype and acute leukaemia [odds ratio (OR) = 1.69, 95% confidence interval (CI) 1.17-2.43], a risk also found in AML and ALL. No interaction was found with smoking. However, a significant age-related association between CYP2D6 polymorphism and acute myeloid leukaemia implied that the excess risk was confined to persons aged 40 years and over (OR 2.38, 95% CI 1.53-3.71). Amongst AML cases, increased odds ratios were observed in both de-novo (OR 1.54, 95% CI 1.02-2.32) and secondary leukaemia (OR 2.83, 95% CI 0.91-8.77), and among patients with a chromosomal abnormality (OR 2.00, 95% CI 1.11-3.61). An increased risk was found for the CYP2C19 poor metabolizer phenotype (OR 1.68, 95% CI 0.97-2.92) which was also present in AML and ALL. For this CYP450 locus, an increased risk was suggested in secondary leukaemia (OR 2.67, 95% CI 0.44-16.3) and amongst AML cases with a chromosomal abnormality (OR 6.72, 95% CI 2.22-20.4). No difference in CYP1A1 genotype distribution was found for acute leukaemia, AML, ALL or any other diagnostic classification group used. No significant interactions between CYP2D6, CYP2C19 or CYP1A1 were found.