To investigate the effects of a deficiency of Abcg8/sterolin-2 on the genes that regulate sterol metabolism, quantitative RT-PCR was performed looking at the expression levels of Abcg5, Abcg8, Hmgr, Cyp7a1, Abca1, Mdr2, Lxr, Srebp-1c, and Srebp-2 mRNA in the livers of mice fed a regular chow diet (Figure 4a). As expected, Abcg8 mRNA expression levels were undetectable in the Abcg8-/- mice and were reduced by ~50% in the heterozygous mice, relative to wild-type mice. Interestingly, by quantitative RT-PCR, the mRNA expression of Abcg5 in the knock-out mice was also reduced by more than 60% compared to the wild-type mice, although no changes were noted in the heterozygous mice. Expression of HMG-CoA reductase mRNA was decreased by ~50% and ~80% in the heterozygote and knockout mice respectively, in keeping with limited observations in human patients with this disorder [7].