validation study. We applied five criteria for selection of genes from this functional category: 1) Statistical differences in gene expression (individual gene or over-represented pathway) related to predisposition to alcohol consumption in mice (Mulligan et al., 2006); 2) Statistical differences in gene expression in a rat or human study (Flatscher-Bader et al., 2008 Kimpel et al., 2007; Liu et al., 2006); 3) Availability of knockout mice; 4) Functional commonality and 5) Absence of publications linking the genes to alcohol consumption. This resulted in four genes that fulfilled all criteria and two genes that fulfilled three criteria and were found only in the Mulligan et al. (2006) data (Table 1). Thus, we evaluated null mutant mice for six genes: B2m (beta-2 microglobulin), Cd14 (cluster of differentiation 14 or CD14 antigen), Il1rn (interleukin 1 receptor antagonist, also known as IL-1ra and IRAP), Il6 (interleukin 6), Ctss (cathepsin S) and Ctsf (cathepsin F).
