[Sex ratio in myelocele and anencephaly]

The secondary sex ratio in 254 probands with anencephaly and spina bifida, their 138 sibs and 2492 relatives (sibs of mothers and fathers, sibs of grandmothers and grandfathers) was studied. In anencephaly, girls prevail (males - 29%, p less than 0.001), and in sibs of anencephalic male probands there is a predominance of males (males - 71%, p less than 0.05). The change in the sex ratio of the probands with spina bifida and their sibs is not significant. In anencephaly, a significant decrease of a male part is also found in the sibs of the probands' mothers (males - 42%, p less than 0.01), in the sibs of the probands' grandmothers and grandfaterhs by the maternal line (males - 45%, p less than 0.025 and males - 42%, p less than 0.01), and also in the sibs of the probands' grandmothers by the paternal line (males - 40%, p less than 0.01). A significant increase in the incidence of the spina bifida occulta is noted among the probands' fathers. The data obtained are in accordance with the hypothesis suggested by Timpson, on the three loci (linked with the X-chromosome by two loci) heredity of the neural tube defects.