Miller R W
Clinical Epidemiology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
Health Phys. 1988 Aug;55(2):295-8. doi: 10.1097/00004032-198808000-00022.
Small head size and mental retardation have been known as effects of intrauterine exposure to ionizing radiation since the 1920s. In the 1950s, studies of Japanese atomic-bomb survivors revealed that at 4-17 wk of gestation, the greater the dose, the smaller the brain (and head size), and that beginning at 0.5 Gy (50 rad) in Hiroshima, mental retardation increased in frequency with increasing dose. No other excess of birth defects was observed. Otake and Schull (1984) pointed out that the period of susceptibility to mental retardation coincided with that for proliferation and migration of neuronal elements from near the cerebral ventricles to the cortex. Mental retardation could be the result of interference with this process. Their analysis indicated that exposures at 8-15 wk to 0.01-0.02 Gy (1-2 rad) doubled the frequency of severe mental retardation. This estimate was based on small numbers of mentally retarded atomic-bomb survivors. Although nuclear accidents have occurred recently, new cases will hopefully be too rare to provide further information about the risk of mental retardation. It may be possible, however, to learn about lesser impairment. New psychometric tests may be helpful in detecting subtle deficits in intelligence or neurodevelopmental function. One such test is PEERAMID, which is being used in schools to identify learning disabilities due, for example, to deficits in attention, short- or long-term memory, or in sequencing information. This and other tests could be applied in evaluating survivors of intrauterine exposure to various doses of ionizing radiation. The results could change our understanding of the safety of low-dose exposures.
自20世纪20年代以来，人们就知道小头症和智力迟钝是子宫内暴露于电离辐射的影响。20世纪50年代，对日本原子弹幸存者的研究表明，在妊娠4至17周时，剂量越大，大脑（和头部尺寸）越小，而且在广岛，从0.5 Gy（50拉德）开始，智力迟钝的频率随剂量增加而增加。未观察到其他出生缺陷的增加。大竹和舒尔（1984年）指出，智力迟钝的易感性时期与神经元从脑室附近向皮质增殖和迁移的时期一致。智力迟钝可能是这一过程受到干扰的结果。他们的分析表明，在8至15周时暴露于0.01至0.02 Gy（1至2拉德）会使严重智力迟钝的频率增加一倍。这一估计是基于少数智力迟钝的原子弹幸存者得出的。尽管最近发生了核事故，但新病例有望极为罕见，无法提供关于智力迟钝风险的更多信息。然而，有可能了解到较轻的损害。新的心理测量测试可能有助于检测智力或神经发育功能的细微缺陷。其中一项测试是PEERAMID，它正在学校中用于识别例如由于注意力、短期或长期记忆或信息排序缺陷导致的学习障碍。这项测试和其他测试可用于评估子宫内暴露于各种剂量电离辐射的幸存者。结果可能会改变我们对低剂量暴露安全性的理解。
