Genes from both the mother and father can trigger pre-eclampsia, finds a study published online by the BMJ today.

Pre-eclampsia is a serious condition where abnormally high blood pressure and other disturbances develop in the second half of pregnancy. It occurs in 3-5% of pregnancies and is dangerous for both mother and child.

Researchers in Norway used birth registry data to study whether men and women who are born after pre-eclamptic pregnancies pass on this risk to the next generation, compared with those who had no family history of pre-eclampsia.

They found that daughters of women who had pre-eclampsia during pregnancy had more than twice the risk of pre-eclampsia themselves compared with other women. Men born after a pregnancy complicated by pre-eclampsia also had a moderately increased risk of fathering a pre-eclamptic pregnancy.

These associations were stronger for the more severe types of pre-eclampsia.

Sisters of affected men or women, but who were not themselves born after a pre-eclampic pregnancy, also had an increased risk. However, for brothers, the risk of fathering a pre-eclamptic pregnancy was similar to that in men with no family history.

This suggests that maternal susceptibility can pass from mother to daughter but not from mother to son, write the authors.

These results support the theory that both the mother's and the father's genes contribute to the risk of pre-eclampsia, say the authors. The risk through affected mothers is higher because they carry their mother's susceptibility genes and also transmit independent genetic risk factors to their unborn child. The risk through affected fathers is lower because fathers transmit only fetal risk genes.