BACKGROUND: Type III hyperlipoproteinemia (HLP), a disorder associated with a 
high incidence of premature cardiovascular diseases, is characterized by the 
accumulation of remnant lipoproteins in the plasma. The primary genetic defect 
in patients with type III HLP is the presence of apolipoprotein E2 (apoE2), an 
isoform of apoE, and accumulation of remnant lipoproteins in the plasma has been 
thought to be attributable to the presence of apoE2, which bind poorly to low 
density lipoprotein receptors, resulting in defective remnant lipoprotein 
clearance. On the other hand, the activity of hepatic lipase (HL), the enzyme 
that plays a pivotal role in the removal of remnant lipoproteins, in type III 
HLP has not been investigated.
METHODS: We examined post-heparin plasma lipoprotein lipase (LPL) and HL 
activities in 7 patients with type III HLP. The activities of HL and LPL in 
post-heparin plasma were measured separately by an immunochemical method using 
antiserum specifically directed against HL.
RESULTS: The post-heparin plasma HL activity was significantly reduced, while 
the LPL activity was normal.
CONCLUSIONS: Reduced HL activity may account, at least in part, for the 
accumulation of remnant lipoproteins in the plasma, a characteristic feature of 
type III HLP.