PCSK9 and Wilson disease: We quantified the expression of key genes implicated in cholesterol homeostasis in the liver: mRNA levels of the rate-limiting cholesterol synthesis enzyme HMG CoA reductase (Fig. 2A), LDL receptors (LDLR) responsible for LDL uptake (Fig. 2B), apolipoprotein B (apoB), a necessary partner for LDL in receptor binding (Fig. 2C), and proprotein convertase subtilisin kexin type 9 (PCSK9) that mediates degradation of the LDLR (Fig. 2D) were unaffected by WD in both mouse strains.