Lipoproteins and Apolipoproteins

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Important inherited hyperlipoproteinemias

Dyslipidemia

Protein defect

Elevated lipoproteins

Major manifestations

Familial chylomicronemia syndrome
(type I)
  • Lipoprotein lipase
  • ApoC-2
  • Chylomicrons
  • Acute pancreatitis
  • Lipemia retinalis
  • Eruptive xanthomas

Familial hypercholesterolemia (type II A)
  • LDL receptor
  • ApoB-100
  • LDL
  • Premature atherosclerosis
  • Tendon xanthomas
  • Xanthelasmas

Familial dysbetalipoproteinemia
(type III)
  • ApoE
  • Chylomicron & VLDL remnants
  • Premature atherosclerosis
  • Tuboeruptive & palmar xanthomas

Familial hypertriglyceridemia
(type IV)
  • Polygenic
  • VLDL
  • Associated with coronary disease, pancreatitis & diabetes

 

Familial dysbetalipoproteinemia (type III hyperlipoproteinemia) is characterized by xanthomas and premature coronary and peripheral vascular disease.  It is an autosomal recessive disorder that is clinically more severe in patients with other conditions affecting lipoprotein metabolism (eg, diabetes, hypothyroidism).

The primary defects in familial dysbetalipoproteinemia are in ApoE3 and ApoE4, apolipoproteins found on the triglyceride-rich lipoproteins (chylomicrons and VLDLs) that are responsible for binding hepatic apolipoprotein receptors.  Without ApoE3 and ApoE4, the liver cannot efficiently remove chylomicrons and VLDL remnants from the circulation, causing their accumulation in the blood and resultant elevations in cholesterol and triglyceride levels.