A new type of familial hypercholesterolaemia.

Two members of a family (proband and daughter) with hypercholesterolaemia have an abnormal low-density lipoprotein which fails to suppress the activity of a rate-determining enzyme for cholesterol biosynthesis (3-hydroxy-3-methyl glutaryl-CoA reductase) in leucocytes of the patients and controls. However, the proband's leucocytes are inhibited by lipoproteins from other sources demonstrating that the mechanism for cellular regulation of the enzyme is intact. This mutant lipoprotein may have a role in the production of hypercholesterolaemia.