A gene variant affects ability to quit smoking during pregnancy

A common genetic variant has been identified that may help explain why some mothers-to-be find it harder to quit smoking when pregnant than others. The research, carried out in the UK, is published in the journal Human Molecular Genetics.

Smoking during pregnancy can cause many problems for the child, including the increased risk of low birth weight, premature birth and stillbirth, as well as cot death - a message that is clearly and strongly stated by public health services. Statistics show that women are more likely to give up smoking during pregnancy than at any other time in their lives due to considerable health and social pressures. Some women, however, continue to smoke while they are pregnant. Other factors can influence whether they quit, such as age, education and whether or not their partners smoke.

This new study was carried out by researchers from the Peninsular Medical School, Exeter, and the University of Bristol, who used data from the Avon Longitudinal Study of Parents and Children and the Exeter Family Study of Childhood Health.

The data looked at 7,845 women of European descent from the South West of England, 2,474 of whom who smoked regularly before they became pregnant. These women were studied to analyse the association between a gene variant and smoking cessation and smoking quantity during pregnancy. The gene variant in question, a variant in a nicotinic acetylcholine receptor gene cluster, had been previously linked with greater cigarette consumption.

Overall, 28 per cent of the women said they had given up smoking in the first trimester of their pregnancy. This figure, however, was only 21 per cent in the group of women with two copies of the 'addictive' gene variant compared with 31 per cent in women with two copies of the normal gene. Later on in the third trimester, 47 per cent of women with two copies of the normal gene said they had quit smoking, compared with only 34 per cent of women with two copies of the 'addictive' gene variant.

Dr Rachel Freathy from the Peninsula Medical School and co-author of the research, concludes: 'We were keen to investigate whether the genetic variant that influences increased cigarette consumption also had a role to play as an extra hurdle to quitting smoking during pregnancy, and our study suggests that it does'.

The authors are keen to emphasise that the results should not be used as an excuse avoid giving up smoking during pregnancy, as a large proportion of women with the 'addictive' gene variant still managed to quit.

Co-author Professor Tim Frayling, an expert in human genetics, says that 'there are parallels with the obesity gene in that people think it's a matter of self control but it's more complicated than that. It's clear that some women with two copies of the addictive gene can give up, it just means it's more difficult for some people than others'.