The discovery of NARC-1 by Seidah was the basis for revealing that gain-of-function (GOF) mutations in this gene, leading to higher production, were the cause of familial hypercholesterolemia (i.e., a genetic form of extremely high levels of low-density lipoprotein cholesterol (LDL-C) [35], a critical risk factor for coronary heart disease). This evidence concerns the gene PCSK9 and familial hypercholesterolemia.