Abstract

The twin pairs with spina bifida and or anencephalus collected from the literature by Rogers and Weatherall (1976) form the basis for an argument that the apparent rarity of dizygous twins concordant for these malformations may be due to the breakdown of the interamniotic partition and a subsequent fetus-fetus interaction. It is suggested that this may lead to complete or partial destruction of one twin. When cells survive they may form teratoma or patches of anomalous skin cover. The hypothesis that monozygous twins concordant for these defects may form double monsters is re-stated. The present hypothesis predicts that the incidence of pineal and intraspinal teratoma will vary in time and place with anencephalus and spina bifida, and that the scalp type hairs found over or around spina bifida may prove, in male infants, to have female chromosomes.