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Thursday, 26 July, 2001, 22:51 GMT 23:51 UK
Miscarriage gene identified
Pregnant woman
Some women suffer repeated miscarriages
Scientists have identified a gene which appears to trigger repeated unexplained miscarriages in some women.

Nearly a fifth of all pregnancies end in miscarriages - but up to 2% of women suffer three or more consecutive pregnancy losses before 20 weeks.


It does confer a small but significantly increased risk

Professor Clemens Tempfer
A significant proportion of these miscarriages remain unexplained.

Researchers from the University of Vienna have found evidence that a variation in a gene called nitric oxide synthase (NOS) could be at least partly to blame. 

NOS controls the way the blood vessels function by influencing the way that the muscles in the lining of the vessels relax.

It does this by synthesising a chemical called nitric oxide.

A lack of this chemical is thought to be responsible for causing blood vessel disease and damage.

It may be that a defective version of the NOS gene increases the risk of miscarriage by failing to produce nitric oxide in sufficient quantity to enable the blood vessels in the placenta to develop properly, thus starving the developing foetus of the nutrients it needs to survive.

Women with this particular variation of the gene were found to be at a 60% greater risk of recurrent miscarriage.

Increased risk

The researchers compared a group of 105 women who had all suffered recurrent spontaneous miscarriages with a carefully matched control group of 91 postmenopausal women who had never had a miscarriage and who had given birth at least twice.

They found the women who had miscarried were much more likely to carry the variant form of the NOS gene.

Lead researcher Professor Clemens Tempfer said: "Given also the role that nitric oxide deficiency plays in high blood pressure, haemorrhage, vascular spasms and infarction [heart attack], it's reasonable to speculate that carriers of an NOS3 polymorphism are at increased risk for impaired placental function.

"Displaying this polymorphism is not necessary or sufficient on its own for the development of unexplained recurrent miscarriages, but our data indicate that it does confer a small but significantly increased risk.

"Identifying a link between unexplained recurrent miscarriages and a specific variant of a gene involved in the regulation of placental function and the stability of the vascular 'environment' is going to give us further insight into this syndrome and more information about susceptible women."

Mr Roy Farquharson, a consultant obstetrician and gynaecologist at Liverpool Women's Hospital, told BBC News Online that the NOS gene had also been implicated other pregnancy complications.

These include abruption, where the placenta separates from the uterus wall, and the potentially life-threatening condition pre-eclampsia.

He said: "This research casts another ray of light on a relatively unknown area, but a direct cause and effect has yet to be established.

"We are focussing more and more on the function of the afterbirth in the early stages of pregnancy as a possible cause of unexplained miscarriage."

Ruth Bender Atik, national director of the Miscarriage Association, said: "Women and their partners who suffer recurrent miscarriage are often desperate to know why this is happening to them."

The research is published in the journal Human Reproduction.

See also:

13 Jan 00 | Health
Genetic miscarriage risk
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