Mutations and polymorphisms in the proprotein convertase subtilisin kexin 9 (<i>PCSK9</i>) gene in cholesterol metabolism and disease

Hypercholesterolemia is one of the major causes of coronary heart disease (CHD). The genes encoding the low-density lipoprotein receptor and its ligand apolipoprotein B, have been the two genes classically implicated in autosomal dominant hypercholesterolemia (ADH). Our discovery in 2003 of the first mutations of the proprotein convertase subtilisin kexin 9 gene (PCSK9) causing ADH shed light on an unknown actor in cholesterol metabolism that since then has been extensively investigated. Several PCSK9 variants have been identified, some of them are gain-of-function mutations causing hypercholesterolemia by a reduction of low-density lipoprotein (LDL) receptor levels; while others are loss-of-function variants associated with a reduction of LDL-cholesterol (LDL-C) levels and a decreased risk of CHD. In this review, we focus on reported variants, and their biological, clinical, and functional relevance. We also highlight the spectrum of hypercholesterolemia or hypobetalipoproteinemia phenotypes that are already associated with mutations in PCSK9. Finally, we present future prospects concerning this therapeutic target that might constitute a new approach to reduce cholesterol levels and CHD, and enhance the effectiveness of other lipid-lowering drugs.