Technical Report No. 13-88
Prenatal exposure to ionizing radiation and subsequent development of seizures
Dunn K, Yoshimaru H, Otake M, Annegers JF, Schull WJEditor’s note: Publications based on this report were published in Congenital Anomalies 29:309-20, 1989, and Am J Epidemiol 131:114-23, 1990.
Summary
The occurrence of seizures is a frequent sequela of impaired brain development, and therefore could be expected to affect more children with radiation-related brain damage than children who are not brain-damaged. The present report deals with the incidence and type of seizures among survivors prenatally exposed to the atomic bombings of Hiroshima and Nagasaki, and their association with specific stages of prenatal development at the time of irradiation. Histories of seizures were obtained at biennial routine clinical examinations starting at the age of 2 years. These clinical records were used to classify seizures as febrile or unprovoked (without precipitating cause). Fetal dose was taken to equal dose in the maternal uterus, according to the DS86 dosimetry.
Seizures were not recorded among individuals exposed 0-7 weeks after fertilization at doses higher than 0.10 Gy. After irradiation at 8-15 weeks after fertilization, the incidence of seizures was highest among individuals with doses exceeding 0.10 Gy and was linearly related to the level of fetal exposure. This is true for unprovoked seizures as well as all seizures regardless of the presence of fever or precipitating causes. When the 22 cases of severe mental retardation were excluded, the increase in seizures was only suggestively significant and then only for unprovoked seizures. After exposure at later stages of development, there was no increase in recorded seizures.
The risk ratios for unprovoked seizures, following exposure during the 8th through the 15th week after fertilization, are 4.4 (90% confidence interval: 0.5-40.9) after 0.10-0.49 Gy and 24.9 (4.1-191.6) after 0.50 Gy or more when the mentally retarded are included, and 4.4 (0.5-40.9) and 14.5 (0.4-199.6), respectively, when they are excluded.
The occurrence of seizures is a frequent sequela of impaired brain development, and therefore could be expected to affect more children with radiation-related brain damage than children who are not brain-damaged. The present report deals with the incidence and type of seizures among survivors prenatally exposed to the atomic bombings of Hiroshima and Nagasaki, and their association with specific stages of prenatal development at the time of irradiation. Histories of seizures were obtained at biennial routine clinical examinations starting at the age of 2 years. These clinical records were used to classify seizures as febrile or unprovoked (without precipitating cause). Fetal dose was taken to equal dose in the maternal uterus, according to the DS86 dosimetry.
Seizures were not recorded among individuals exposed 0-7 weeks after fertilization at doses higher than 0.10 Gy. After irradiation at 8-15 weeks after fertilization, the incidence of seizures was highest among individuals with doses exceeding 0.10 Gy and was linearly related to the level of fetal exposure. This is true for unprovoked seizures as well as all seizures regardless of the presence of fever or precipitating causes. When the 22 cases of severe mental retardation were excluded, the increase in seizures was only suggestively significant and then only for unprovoked seizures. After exposure at later stages of development, there was no increase in recorded seizures.
The risk ratios for unprovoked seizures, following exposure during the 8th through the 15th week after fertilization, are 4.4 (90% confidence interval: 0.5-40.9) after 0.10-0.49 Gy and 24.9 (4.1-191.6) after 0.50 Gy or more when the mentally retarded are included, and 4.4 (0.5-40.9) and 14.5 (0.4-199.6), respectively, when they are excluded.