
congenital malformations of c.n.s.
it seems that only a small proportion of malformations of
the central nervous system can be explained in simple genetical
terms and that most are dependent, to some extent at least,
on environmental factors.  the nature of these has yet to be
determined.  dr. williamson found that the maternal aunts,
uncles, and cousins of her index cases of anencephalus and
spina bifida were more frequently affected than the paternal
relatives were.  she suggested that mothers of affected
children had some genetic factor which modifies the intra-
uterine environment and thus predisposes the embryo to these
malformations.  such a hypothesis opens up interesting
possibilities, but before accepting it one would have to be
satisfied that the higher incidence in maternal relatives is
not merely due to the fact that the history is obtained in
most cases from the mother.
