In 1976, since no techniques were available for direct screening of DNA mutations, RERF used two kinds of protein alterations as potential indicators of mutation. One was a rare electrophoretic variant arising from base substitution mutations and was detected by one-dimensional electrophoresis. The other was an enzyme-deficient protein variant caused by deletion mutations.

Over ten years, nearly 24,000 children of LSS survivors or controls were screened for electrophoretic variants of 30 blood proteins (Table 1); 10,000 of these children were also tested for enzyme-deficient variants (Table 2). The children were classified into two groups according to the combined parental gonadal dose of each child, either 0.01 Gy or greater (exposed group) or below 0.01 Gy (control group). A total of 1,233 electrophoretic variants and 47 enzyme-deficient variants were detected. Studies of parents showed that most variants were pre-existing and that only six electrophoretic variants and one enzyme-deficient variant originated from new mutations in parental germ cells. In the study of electrophoretic variants, two new mutations were detected in the exposed group and four in controls. The only enzyme-deficient mutant found was in the exposed group.

Table 1. Results of screening for electrophoretic protein variants

*Weighted mean dose 0.49 Gy

Table 2. Results of screening for enzyme-deficient protein variants

These results provide no evidence for radiation-induced germ cell mutations. This may not be surprising since the enzyme-deficiency study was too small for adequate statistical power to detect radiation effects and since it later became clear that radiation only rarely causes altered base substitutions and hence altered electrophoretic mobility. Direct screening for DNA mutations is now being undertaken.

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