PCSK9 and familial hypercholesterolemia: However, this usually depends on whether the PCSK9 mutation provides a (1) GOF, leading to FH due to the increase in LDLR degradation, or (2) an LOF leading to hypercholesterolemia associated with the decrease in LDLR degradation (Noguchi et al., 2010; Mabuchi et al., 2011).