Smoking has been found to be associated with an increased risk of depression, although the direction of causality is unclear. Munafo et al (2008) found that in ALSPAC smoking cessation was associated with a reduction in depression symptom score. However, this finding could be explained by confounding by other factors, or reverse causation where women who are feeling more positive are more likely to stop smoking. Freathy et al (2009) have identified a genetic variant in the CHRNA5-CHRNA3-CHRNB4) gene cluster which is strongly associated with quitting smoking in pregnancy in ALSPAC, but which is not associated with typical confounding factors.

We would like to use this variant to carry-out a Mendelian randomization analysis to determine whether a causal association between quitting smoking during pregnancy and a reduction in depressive symptom score exists.

We already have data on depression scores and potential confounders which has been used for another analysis of folate and depression so we would only require the genotype data in order to carry-out this analysis.

References:

Freathy RM, Ring SM, Shields B, Galobardes B, Knight B, Weedon MN, Smith GD, Frayling TM, Hattersley AT.A common genetic variant in the 15q24 nicotinic acetylcholine receptor gene cluster (CHRNA5-CHRNA3-CHRNB4) is associated with a reduced ability of women to quit smoking in pregnancy. Hum Mol Genet. 2009 May 9. [Epub ahead of print]

Munafo MR, Heron J, Araya R. Smoking patterns during pregnancy and postnatal period and depressive symptoms. Nicotine Tob Res. 2008 Nov;10(11):1609-20.