Hyperlipidemia is a condition characterized by the presence of excess amount of lipids in the bloodstream. It may also pertain to the abnormally high level of lipoproteins in the blood although the term hyperlipoproteinemia is sometimes used to refer specifically to this condition. The opposite condition of hyperlipidemia is hypolipidemia wherein the level of lipids (or lipoproteins) in the blood is atypically low. Both of them are forms of dyslipidemia, which is defined as any abnormality in the lipid level in the blood. Hyperlipidemia, though, is more common than hypolipidemia, especially in the developed countries where diet and lifestyle cause elevated lipids. There are two types of hyperlipidemias: primary and secondary. Primary (or familial) hyperlipidemia is associated with genetic factors and it is further classified into the following types:
- Type Ia (Buerger-Gruetz syndrome), Type Ib (familial apoprotein CII deficiency), and Type Ic (chylomicronemia). Type I is caused by an increase in chylomicrons, which in turn is due to a decrease in lipoprotein lipase (LPL), an altered apolipoprotein C2, or a circulating inhibitor of LPL, respectively.
- Type II, the most common form, is caused by an increase in low-density lipoprotein (LDL). Two subtypes occur: Type IIa (familial hypercholesterolemia) and Type IIb (familial combined hyperlipidemia). Type IIa is due to a deficiency in LDL receptor. In Type IIb, the condition is accompanied by very-low-density lipoprotein (VLDL) elevations due to increased apolipoprotein B.
- Type III (familial dysbetalipoproteinemia) is characterized by an elevated intermediate-density lipoprotein due to a defect in apolipoprotein E2.
- Type IV (familial hypertriglyceridemia) is caused by abnormally high level of VLDL due to increased production while decreased elimination of VLDL.
- Type V (mixed hyperlipoproteinemia familial or mixed hyperlipidemia) is characterized by elevated VLDL and chylomicrons due to increased VLDL production and decreased LPL.
Secondary (or acquired) hyperlipidemia is essentially non-genetic but occurs as a consequence of other medical conditions, such as diabetes mellitus, kidney failure, and kidney failure, or the use of thiazide diuretics, beta blockers, and other drugs.
Variant: hyperlipidaemia. Synonyms: hyperlip(a)emia, hyperlipoidemia, lip(a)emia, lipid(a)emia, lipoid(a)emia.
- Chait, A. & Brunzell, J. D. (June 1990). "Acquired hyperlipidemia (secondary dyslipoproteinemias)". Endocrinol. Metab. Clin. North Am. 19 (2): 259–78.
- Fredrickson, D. S. & Lees, R. S. (1965). "A system for phenotyping hyperlipoproteinemia" (PDF). Circulation. 31 (3): 321–27. Retrieved from http://circ.ahajournals.org/cgi/reprint/31/3/321
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