By day 11 of a Leiden pregnancy, a fetus with paternal mutations in anticoagulant genes (left) is more decayed than its sibling (right).

A pregnancy disorder that leads to an early loss of the fetus is linked to mutations that increase the mother's tendency to form blood clots. But Sood et al. (page 1049) now find that maternal genes are only partly responsible. The rest of the blame falls on genetic defects that the fetus inherits from the father.

Recurrent miscarriages are associated with mutations known as Leiden polymorphisms, which prevent the factor V coagulant from being destroyed by the anticoagulation machinery. The assumption has been that clots formed in the placenta of Leiden mothers might cripple fetal growth by blocking nutrient supply.

Examination of placental tissue from Leiden mothers, however, shows no correlation between placental clotting and fetal loss. And female mice with...

The Rockefeller University Press
2007
The Rockefeller University Press
2007
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