Is It Ever Wise to Edit Wild-Type Alleles? Engineered CRISPR Alleles Versus Millions of Years of Human Evolution.

Abstract

The tremendous burden of lipid metabolism diseases, coupled with recent developments in human somatic gene editing, has motivated researchers to propose population-wide somatic gene editing of PCSK9 (proprotein convertase subtilisin/kexin type 9) within the livers of otherwise healthy humans. The best-characterized molecular function of PCSK9 is its ability to regulate plasma LDL (low-density lipoprotein) levels through promoting LDL receptor degradation. Individuals with loss-of-function PCSK9 variants have lower levels of plasma LDL and reduced cardiovascular disease. Gain-of-function variants of PCSK9 are strongly associated with familial hypercholesterolemia. A new therapeutic strategy delivers CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats; CRISPR-associated protein 9) specifically to liver cells to edit the wild-type alleles of PCSK9 with the goal of producing a loss-of-function allele. This direct somatic gene editing approach is being pursued despite the availability of US Food and Drug Administration-approved PCSK9 inhibitors that lower plasma LDL levels. Here, we discuss other characterized functions of PCSK9 including its role in infection and host immunity. We explore important factors that may have contributed to the evolutionary selection of PCSK9 in several vertebrates, including humans. Until such time that more fully understand the multiple biological roles of PCSK9, the ethics of permanently editing the gene locus in healthy, wild-type populations remains highly questionable.