Several parameters of
lipoprotein metabolism were examined in 38 men with primary
hypertriglyceridemia (phenotype IV). Family investigation showed that 17 men had
familial combined hyperlipidemia (FCH), seven had
familial hypertriglyceridemia (FHT), and 14 had unclassified
hypertriglyceridemia (UNC). In all three groups, plasma
high density lipoprotein (
HDL) cholesterol and the concentrations of
apolipoprotein A-I and A-II were decreased, and
apolipoprotein B was increased, each to the same extent. These results are compatible with an increased risk of
cardiovascular disease in both FCH and FHT patients. The mean concentration of
LDL cholesterol and the ratio of
LDL to
HDL cholesterol were significantly higher in FCH subjects, which could explain their increased risk.
Postheparin lipoprotein lipase and hepatic
lipase were the same in both groups. Determination of
apolipoprotein C composition, which may modulate
lipoprotein lipase activity, did not reveal any abnormalities in the different groups. In both FCH and FHT, the mean turnover rate of plasma
triglycerides was almost twice normal, indicating that overproduction of plasma
triglyceride plays an important role in both disorders. However, there was an overlap with normal controls, indicating impaired
triglyceride removal in some subjects. The underlying mechanism of
hypertriglyceridemia in FCH and FHT therefore seems to be heterogeneous.