REVIEW - RADIATION-RELATED BRAIN-DAMAGE AND GROWTH-RETARDATION AMONG THE PRENATALLY EXPOSED ATOMIC-BOMB SURVIVORS

Many studies of prenatally exposed survivors of the atomic bombings of Hiroshima and Nagasaki have shown that exposure to ionizing radiation during gestation has harmful effects on the developing human brain. D ata on the occurrence of severe mental retardation as well as variatio n in intelligence quotient (IQ) and school performance show significan t effects on those survivors exposed 8-15 and 16-25 weeks after ovulat ion. Studies of seizures, especially those without a known precipitati ng cause, also exhibit a radiation effect in survivors exposed 8-15 we eks after ovulation. The biologic events that subtend these abnormalit ies are still unclear. However, magnetic resonance imaging of the brai ns of some mentally retarded survivors has revealed a large region of abnormally situated gray matter, suggesting an abnormality in neuronal migration. Radiation can induce small head size as well as mental ret ardation, and a review of the relationship between small head size and anthropometric measurements, such as height, weight, sitting height a nd chess circumference, shows that individuals with small head size ha ve smaller anthropometric measurements than normocephalics. This sugge sts that radiation-related small head size is related to a generalized growth retardation. Finally, the issue of a threshold in the occurren ce of one or more of these effects, both heuristically and From a regu latory perspective, remains uncertain. Simple inspection of the data o ften suggests that a threshold may exist, but little statistical suppo rt for this impression can be advanced, except in the instance of ment al retardation.