On the pathogenesis of acquired hypo-beta-lipoproteinemia. A case associated with sideroblastic anemia.

A 71-year-old previously hypercholesterolemic woman developed gradually severe hypocholesterolemia of 1.55 mmol/l. Simultaneously she developed progressive sideroblastic anemia, altered erythrocyte morphology and defective platelet function. Hypo-beta-lipoproteinemia was demonstrated with abnormal lipid composition of both very low density (VLDL), low density (LDL) and high density lipoprotein (HDL) fractions. Other plasma lipids, as well as erythrocyte lipids, were normal. The fractional catabolic rate of homologous 125I-LDL was increased to 4-5-fold, while its rate of synthesis was normal. The patient's serum contained autoantibodies directed against LDL. It is concluded that her hypo-beta-lipoproteinemia was due to autoantibodies towards LDL causing an increased catabolism without any concomitant effect on the rate of LDL synthesis. It is suggested that acquired hypo-beta-lipoproteinemia can be subdivided into two types, one in which the primary defect is an increased catabolism due to immunoelimination, and another in which the primary defect is a decreased rate of LDL synthesis.