Familial hypercholesterolemia (FH) due to a pathogenic mutation in one of the five thus far identified genes that take part in cholesterol metabolism (LDL Receptor (LDLR), apolipoprotein B (APOB), PCSK-9, apolipoprotein E (APOE), signal transducing adaptor family member 1 (STAP1), and LDL receptor adaptor protein 1 (LDLRAP1)) is a monogenic disease and is probably the most harmful form of hypercholesterolemia. The gene discussed is LDLR; the disease is familial hypercholesterolemia.