Plasma
lipids,
lipoproteins, tissue
lipoprotein lipase (LPL) and hepatic
lipase (H-TGL) were studied in 7 patients with
familial hyperchylomicronemia from four different families. Their first-degree relative were also studied. The patients were heterogeneous for the genetic defect; LPL activity was absent in five patients (LPL deficiency) but normal in two. However, these two did not have
apo C-II, the physiological activator of LPL (C-II deficiency). There were no significant differences in the clinical picture between patients with LPL deficiency and C-II deficiency. In both mutants, marked
hypertriglyceridemia was due to an accumulation of
lipoproteins of density less than 1.006 g/ml. The
LDL fraction was very reduced and abnormal in composition, presenting a CH/TG ratio of 0.5. The plasma
apolipoprotein B (
apo B) level was low (67 +/- 5.5 mg/dl) and was transported mainly in the VLDL fraction (26 +/- 3.2 mg/dl) rather than in the
LDL fraction (15 +/- 1.4 mg/dl). Very low levels of
cholesterol and
apolipoprotein A-I in HDL subfractions HDL2 and HDL3 were also recorded. Only 3 out of the 24 first-degree relatives of patients with LPL deficiency showed even a small increase in plasma
triglycerides, but 15 had low or low to normal LPL values. H-TGL levels were normal in all subjects. The 4 first-degree relatives of C-II deficiency patients showed normal levels of plasma
lipids. LPL and H-TGL, and 2 children of 1 patient showed normal distribution of
apo C peptides in their VLDL. A block in
chylomicron catabolism, due to the absence of LPL or
apo C-II, may lead to a massive accumulation of
lipoproteins with a density less than 1.006 g/ml, and a drastic reduction in the
LDL and HDL fractions. Low LPL values in the first-degree relatives of LPL deficiency patients might represent a
biochemical marker for healthy carriers of LPL deficiency.