Analysis of somatic cell mutations at the glycophorin A locus in atomic bomb survivors: a comparative study of assay methods.

The glycophorin A (GPA) assay for in vivo somatic cell mutations was performed on blood samples from 39 survivors of the atomic bomb at Hiroshima. Parallel analyses were performed at two laboratories using three different GPA assay methods to enumerate cells lacking expression of either the M- or N-allele of GPA. All assay methods yielded significant dose-dependent increases in hemizygous GPA variant cell frequencies (VFs) and smaller increases in homozygous VFs. The slopes of the fitted linear dose-response functions did not differ significantly among assay methods used in the present study, or from slopes obtained in a study reported previously. The version of the assay described most recently (BR6) appears best suited for future studies because the assay has a higher precision than earlier methods. Variant frequencies from different assay methods measuring the same variant cell type agreed with each other better than with the estimated dose, suggesting that the imprecision in the assay is not primarily responsible for VFs that differ from the fitted dose response. Consistent deviations from the dose response were seen for some individuals, suggesting either errors in dose estimates for these individuals or interindividual differences in susceptibility or other exposures. For the study population as a whole, however, discrepancies between assays for M-loss and N-loss variants suggest stochastic factors may have an important effect on individual VFs for A-bomb survivors.