Technical Report No. 3-88
Effect on intelligence test score of prenatal exposure to ionizing radiation in Hiroshima and Nagasaki: A comparison of the T65DR and DS86 dosimetry systems
Schull WJ, Otake M, Yoshimaru HEditor’s note: A publication based on this report was published in Congenital Anomalies 29:309-20, 1989.
Summary
Analyses of intelligence test scores (Koga) at 10-11 years of age of individuals exposed prenatally to the atomic bombing of Hiroshima and Nagasaki using estimates of the uterine absorbed dose based on the recently introduced system of dosimetry, the Dosimetry System 1986 (DS86), reveal the following: 1) there is no evidence of a radiation-related effect on intelligence among those individuals exposed within 0-7 weeks after fertilization or in the 26th or subsequent weeks; 2) for individuals exposed at 8-15 weeks after fertilization, and to a lesser extent those exposed at 16-25 weeks, the mean tests scores but not the variances are significantly heterogeneous among exposure categories; 3) the cumulative distribution of test scores suggests a progressive shift downwards in individual scores with increasing exposure; and 4) within the group most sensitive to the occurrence of clinically recognizable severe mental retardation, individuals exposed 8 through 15 weeks after fertilization, the regression of intelligence score on estimated DS86 uterine absorbed dose is more linear than with T65DR fetal dose; the diminution in intelligence score under the linear model is 21-29 points at 1 Gy. The effect is somewhat greater when the controls receiving less than 0.01 Gy are excluded, 24-33 points at 1 Gy.
These findings are discussed in the light of the earlier analysis of the frequency of occurrence of mental retardation among the prenatally exposed survivors of the A-bombing of Hiroshima and Nagasaki. It is suggested that both are the consequences of the same underlying biological process or processes.
Analyses of intelligence test scores (Koga) at 10-11 years of age of individuals exposed prenatally to the atomic bombing of Hiroshima and Nagasaki using estimates of the uterine absorbed dose based on the recently introduced system of dosimetry, the Dosimetry System 1986 (DS86), reveal the following: 1) there is no evidence of a radiation-related effect on intelligence among those individuals exposed within 0-7 weeks after fertilization or in the 26th or subsequent weeks; 2) for individuals exposed at 8-15 weeks after fertilization, and to a lesser extent those exposed at 16-25 weeks, the mean tests scores but not the variances are significantly heterogeneous among exposure categories; 3) the cumulative distribution of test scores suggests a progressive shift downwards in individual scores with increasing exposure; and 4) within the group most sensitive to the occurrence of clinically recognizable severe mental retardation, individuals exposed 8 through 15 weeks after fertilization, the regression of intelligence score on estimated DS86 uterine absorbed dose is more linear than with T65DR fetal dose; the diminution in intelligence score under the linear model is 21-29 points at 1 Gy. The effect is somewhat greater when the controls receiving less than 0.01 Gy are excluded, 24-33 points at 1 Gy.
These findings are discussed in the light of the earlier analysis of the frequency of occurrence of mental retardation among the prenatally exposed survivors of the A-bombing of Hiroshima and Nagasaki. It is suggested that both are the consequences of the same underlying biological process or processes.