Haplotypes that were present at different frequencies in the successful vs unsuccessful quitters by chance, not based on ethnic stratification, could conceivably contribute to some of this clustering; we thus view the results reported here [see additional file 1] as nominally-positive genes. Nevertheless, the 221 genes identified by these clustered positive results represent a highly interesting set [see additional file 1]. Seventeen of these genes produce products related to cell adhesion, 39 genes' products relate to enzymatic activities, 37 encode receptors and/or G-protein mechanisms, 5 encode channels, 27 encode transcriptional regulators, 9 genes' products are involved in mechanisms for Mendelian disorders, 12 encode structural proteins, 4 encode proteins involved with vesicle function, 5 encode transporters, 32 encode genes involved with DNA, RNA or protein processing and 34 are genes about which so little is known that we cannot confidently place them in a functional class.
