To make matters more complex, we examined, in a large, population-based twin sample, the association between the key SNPs in this small region and individual items from the Fagerström Test for Nicotine Dependence63. If all the items were reflecting one common underlying genetically influenced trait, they all should have similar associations with these SNPs. Not so. Most of the SNPs had the strongest signals with CPD and time to first cigarette after awakening—typically an item that is quite a sensitive measure of the level of nicotine dependence. But one SNP, rs2869546, had an isolated strong signal from the item about smoking in bed when ill.
