The positions for at least nine possible candidate genes lie within or near the two regions identified by linkage on chromosome 11. These include for 11p: DRD4 (dopamine receptor 4), TPH (tryptophan hydroxylase 1), TH (tyrosine hydroxylase), and CHRNA10 (nicotinic cholinergic receptor-alpha 10), and for 11q23: HTR3A (hydroxytryptamine receptor 3A), HTR3B (hydroxytryptamine receptor 3B), DRD2 (dopamine D2 receptor gene), ANKK1 (ankyrin repeat and kinase domain containing 1), and GRIK4 (ionotropic kainate glutamate receptor 4 gene). The suggestive linkage peak at 123 cM in the Australian (and combined samples) occurs close to DRD2, which has long been considered as a candidate gene in addiction research (c.f.; Blum et al., 1991, and to ANKK1; Neville at al., 2004), with the Taq 1A RFLP polymorphism formally assumed to lie within the DRD2 gene now known to occur within an exon of the protein kinase gene ANKK1. Positive reports of association with various aspects of smoking behavior—including withdrawal symptoms (Robinson et al., 2007), persistent smoking (Morton et al., 2006), and pharmacotherapy response (David et al., 2007a; David et al., 2007b; Han et al., 2008)—have
