Novel DNA sequence variants in the hHR21 DNA repair gene in radiosensitivecancer patients

Purpose: Radiation therapy is an important treatment modality for oncology patients. DNA sequence variants avt eso ar been identified in only a few ge nes in radiosensitive cancer patients. Patients known to be clinically radi osensitive were tested for mutation of a gene involved in DNA double-strand break repair and sister chromatid cohesion-hHR21. Methods and Materials: Clinically radiation-sensitive patients were accrued to the study after giving informed consent. oo samp es were obtained and l ymphoblastoid cell lines established. Reverse transcriptase-polymerase chai n reaction (RT-PCR) was performed to amplify the hHR21 gene, and the DNA pr oduct was sequenced to identify any genetic abnormalities. Northern blot an alysis, cell survival, and growth assays were performed on control cells an d cells with hHR21 variants, and a restriction digest assay was developed t o screen for carriers of a detected gene variant. Results: The DNA sequence of the hHR21 gene was determined in 19 radiation- sensitive cancer patients. In 6 of 19 patients, a thymidine (T) to cytosine {C) transition was detected at position 1440 of the hHR21 open reading fra me (T1440C). This variant did not alter the amino acid sequence and was lik ely to be a polymorphism. One patient with a particularly severe radiation reaction had a second sequence variant immediately adjacent to the first. T his was a guanine (G) to adenine (A) transition (G1441A), resulting in a ch ange of the amino acid sequence {glycine arginine) in a portion of the prot ein conserved in evolution. This suggests that this DNA alteration may be b iologically significant. Restriction digest with the HpaII enzyme confirmed the presence of both sequence variants on the same allele. Conclusions: We describe the first two DNA sequence variants ever found in the hHR21 gene, in patients with mca radiation hypersensitivity. Although n o direct evidence for the involvement of hHR21 alterations in the radiosens itivity of the cancer patients examined has been demonstrated, the possibil ity exists that homozygous mutations or other mutations of this gene could contribute to radiosensitivity. A simple test is described that could be ap plied to screening for these variants in relevant populations. (C) 2001 Els evier Science Inc.