To date, although no data supportive of their involvement in abnormal behavior of Ldlr −/− mice has yet been obtained, our experimental data using Per2 m/m (Ldlr +/+) mice in light and dark in Fig. 1 might indicate that the effect of chronic hypercholesterolemia on behavioral rhythms involve malfunction of the core clock machinery. This evidence concerns the gene LDLR and familial hypercholesterolemia.