Increased risk for myelodysplastic syndromes in individuals with glutathione transferase theta 1 (GSTT1) gene defect.

The glutathione S-transferases (GST) mediate exposure to various cytotoxic and genotoxic agents, including those associated with increased risk of the myelodysplastic syndromes (MDS). Both GST M1 (GSTM1) and GST theta 1 (GSTT1) genes have a "null" variant allele, in which the entire gene is absent. We tested whether the homozygous null genotype of GSTM1 and GSTT1 altered the risk for MDS. In a hospital-based case-control study we analysed lymphocyte or bone-marrow DNA samples from 96 patients with MDS and 201 cancer-free controls of similar age, race, and sex. We have restricted our report to the 92 white MDS patients. We analysed GSTM1 and GSTT1 genotypes by PCR. The frequency of the GSTT1 null genotype was higher among MDS cases (46%) than among controls (16%). Inheritance of the GSTT1 null genotype conferred a 4.3-fold of MDS (odds ratio 4.3, 95% CI 2.5-7.4, p < 0.00001). The GSTM1 null genotype was not associated with increased risk of MDS (odds ratio 0.8, 0.5-1.3). Individuals with the GSTT1 null genotype may have enhanced susceptibility to MDS. The mechanism might involve decreased detoxification of environmental or endogenous carcinogens.