James W H
J Med Genet. 1979 Apr;16(2):129-33. doi: 10.1136/jmg.16.2.129.
A review of the data supports the suggestion of Knox (1974) that the sex ratio and incidence of anencephalics vary together within populations, as they are known to do between populations. There seems some doubts, though, whether Knox was correct in hypothesising that the sex ratio of anencephalics varies with their incidence in relation to the dizygotic twinning rate. The pattern of variation seems to suggest that there are two sorts of cause of anencephaly, one of which is environmental and affects predominantly female embryos. The other may be environmental or genetic, and seems to attack the sexes in roughly equal numbers. If this hypothesis were correct, it would carry implications for the testing of specific teratogens.
对数据的回顾支持了诺克斯（1974年）的观点，即无脑儿的性别比例和发病率在人群中共同变化，就像在不同人群之间已知的那样。不过，诺克斯假设无脑儿的性别比例随其发病率与双卵双胎率的关系而变化是否正确，似乎存在一些疑问。这种变化模式似乎表明无脑儿有两种病因，其中一种是环境因素，主要影响女性胚胎。另一种可能是环境因素或遗传因素，似乎对两性的影响大致相同。如果这个假设正确，它将对特定致畸剂的检测产生影响。
