Two human studies have associated alcohol dependence with human chromosome 15q (Dick et al., 2002; Ehlers et al., 2004) with peak LOD scores >2 near 50 Mb on the current human physical map. Both of these QTLs on human chromosome 15 are syntenic to parts of mouse chromosomes 9 and 2 (Figure 1). Similarly, two groups have identified large alcohol preference QTLs (Etp5 and Ap5q), with LOD scores between 5 and 8, on mouse chromosome 9 (Phillips et al., 1994, 1998; Tarantino et al., 1998). Relying on the robustness of both the mouse and human QTLs, it was possible to narrow the QTL regions of interest in both species based on human/mouse synteny. If these QTLs are in the overlapping syntenic areas, then the focus can be restricted to the homologous candidate QTGs that lie within these narrower intervals (Figure 1). Additionally, since the human chromosome 15 QTLs have better defined regions (sharper peak LOD plots) than the mouse chromosome 9 QTLs, this information can be useful to further narrow the mouse QTL regions beyond just the syntenic regions (Figure 1).
