clathrin and other proteins responsible for the endocytosis of LDL, therefore this mutation inhibits LDL internalization.
* Class 5 mutations give rise to receptors that cannot recycle properly. This leads to a relatively mild phenotype as receptors are still present on the cell surface (but all must be newly synthesised).

Gain-of-function mutations decrease LDL levels and are a target of research to develop a gene therapy to treat refractory hypercholesterolemia.