Abstract

Lipoprotein and apolipoprotein concentrations were determined in 11 homozygous and 9 heterozygous subjects for familial apolipoprotein C-II (Apo C-II) deficiency. Apo C-II was not detectable in the homozygotes, with the exception of 1 subject who possessed immunochemically detectable quantities in one of two samples. Apolipoproteins C-III (Apo C-III) and E (Apo E) were elevated 2-3-fold in 9 of 11 homozygotes. Apo C-III, but not Apo E, correlated with triglyceride levels (1500-4100 mg/dl). However, both Apo C-III and Apo E correlated with the cholesterol levels and one another. Apolipoproteins A-I (Apo A-I), A-II (Apo A-II) and B (Apo B) were reduced to approximately 50-60% of normal values in association with very low levels of cholesterol in high density (HDL; 11 +/- 2 mg/dl) and low density (LDL; 19 +/- 6 mg/dl) lipoproteins in the homozygous subjects. These alterations were associated with a marked decrease in the proportion of plasma Apo C-III associated with HDL. The levels of apolipoprotein D (Apo D) were within the normal range. Nine obligate heterozygotes had Apo C-II concentrations (mean 1.8 +/- 0.5 mg/dl; range 1.2-2.7 mg/dl) which were approximately 40-50% of normal values (mean 2.9 +/- 0.9 mg/dl; range 1.7-5.6 mg/dl). The reduction in absolute amounts of Apo C-II was also reflected in a reduction of the ratio Apo C-II/Apo C-III in very low density lipoproteins (VLDL) and in a reduction in the ability of the sera to activate skim milk lipoprotein lipase. The concentrations of Apo A-II, Apo B, Apo C-III and Apo E were normal. Apo A-I concentrations were normal or slightly low in association with slightly reduced concentrations of HDL cholesterol and a low proportion of plasma Apo C-III in HDL in relation to LDL and VLDL in some heterozygotes. It is concluded that the marked alterations in the apolipoprotein levels in homozygous subjects are primarily a reflection of the deficiency of Apo C-II which results in severe hypertriglyceridemia. In heterozygotes, the partial deficiency of Apo C-II appears to result in a minor disturbance of the clearance of the triglycerides and Apo C-III rich particles but no marked changes in the concentrations of total lipids, lipoproteins and apolipoproteins in fasting plasma.