Heterozygous hypobetalipoproteinemia with fasting chylomicronemia

We describe a disorder in which low-density lipoprotein (LDL)-cholesterol and apolipoprotein B are in low concentration (0.47 mmol/L and 0.28 g/L, respectively) and chylomicrons are still present in plasma after an 18-h fast. The d less than 1.006 fraction was isolated by flotation ultracentrifugation and the apolipoproteins were analyzed by electrophoresis, immunoblotting with anti-apolipoprotein B-100 antiserum, and isoelectric focusing. In the d less than 1.006 fraction of the fasting serum, we found an apolipoprotein B form with the same apparent molecular mass as apolipoprotein B-48 and similar in amount to apolipoprotein B-100 (respective percentages, 46% and 54%). The monosialylated form of the apolipoprotein C-III was severely decreased. After an oral fat load, the repartition of the two species of apolipoprotein B did not change greatly (respective percentages, 60% and 40%), and the concentration of serum triglyceride increased only from 1.20 to 1.65 mmol/L.