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Hyperlipidemia

Encyclopedia : H : HY : HYP : Hyperlipidemia

Hyperlipidemia, hyperlipoproteinemia or dyslipidemia is the presence of elevated or abnormal levels of lipids and/or lipoproteins in the blood. Lipids (fatty molecules) are transported in a protein capsule, and the density of the lipids and type of protein determines the fate of the particle and its influence on metabolism.

Lipid and lipoprotein abnormalities are extremely common in the general population, and are regarded as a highly modifiable risk factor for cardiovascular disease due to the influence of cholesterol, one of the most clinically relevant lipid substances, on atherosclerosis. In addition, some forms may predispose to acute pancreatitis.

Contents

Classification

Hyperlipidemias are classified according to the Fredrickson classification which is based on the pattern of lipoproteins on electrophoresis or ultracentrifugation.Frederickson DS, Lee RS. A system for phenotyping hyperlipidemia. Circulation 1965;31:321-7. PMID 14262568. It was later adopted by the World Health Organization (WHO). It does not directly account for HDL, and it does not distinguish among the different genes that may be partially responsible for some of these conditions. It remains a popular system of classification, but is considered dated by many.

! Hyperlipoproteinemia
! Synonyms
! Problems
! Labs description
! Treatment

! Type I
| Buerger-Gruetz syndrome, Primary hyperlipoproteinaemia, or Familial hyperchylomicronemia
| Decreased lipoprotein lipase (LPL) or altered apolipoprotein C2
| Elevated Chylomicrons
| Diet Control

! Type IIa
| Polygenic hypercholesterolaemia or Familial hypercholesterolemia
| LDL receptor deficiency
| Elevated LDL only
| Bile Acid Sequestrants, Statins, Nicotinic Acid

! Type IIb
| Combined hyperlipidemia
| Decreased LDL receptor and Increased Apo B
| Elevated LDL and VLDL and Triglycerides
| Statins, Nicotinic Acid, Gemfibrozil

! Type III
| Familial Dysbetalipoproteinemia
| Defect in ApoE synthesis
| Increased IDL
| Drug of choice: Gemfibrozil

! Type IV
| Endogenous Hyperlipemia
| Increased VLDL production and Decreased elimination
| Increased VLDL
| Drug of choice: Nicotinic Acid

! Type V
| Familial Hypertriglyceridemia
| Increased VLDL production and Decreased LPL
| Increased VLDL and Chylomicrons
| Nicotinic Acid, Gemfibrozil
Fredrickson classification of Hyperlipidemias

Hyperlipoproteinemia type I

This very rare form (also known as Buerger-Gruetz syndrome, primary hyperlipoproteinaemia, or familial hyperchylomicronemia) is due to a deficiency of lipoprotein lipase (LPL) or altered apolipoprotein C2, resulting in elevated chylomicrons, the particles that transfer fatty acids from the digestive tract to the liver. Its prevalence is 0.1% of the population.

Hyperlipoproteinemia type II

Hyperlipoproteinemia type II, by far the most common form, is further classified into type IIa and type IIb, depending mainly on whether there is elevation in the triglyceride level in addition to LDL cholesterol.

Type IIa

This may be sporadic (due to dietary factors), polygenic, or truly familial as a result of a mutation either in the LDL receptor gene on chromosome 19 (0.2% of the population) or the ApoB gene (0.2%). The familial form is characterized by tendon xanthoma, xanthelasma and premature cardiovascular disease.

Type IIb

The high VLDL levels are due to overproduction of substrates, including triglycerides, acetyl CoA, and an increase in B-100 synthesis. They may also be caused by the decreased clearance of LDL. Prevalence in the population is 10%.

Treatment

While dietary modification is the initial approach, many patients require treatment with statins (HMG-CoA reductase inhibitors) to reduce cardiovascular risk. If the triglyceride level is markedly raised, fibrates may be preferable due to their beneficial effects. Combination treatment of statins and fibrates, while highly effective, causes a markedly increased risk of myopathy and rhabdomyolysis and is therefore only done under close supervision. Other agents commonly added to statins are ezetimibe, nicotinic acid and bile acid sequestrants. There is some evidence for benefit of plant sterol-containing products and ω3-fatty acidsThompson GR. Management of dyslipidaemia. Heart 2004;90:949-55. PMID 15253984.

Hyperlipoproteinemia type III

This form is due to high chylomicrons and IDL (intermediate density lipoprotein). Also known as broad beta disease or dysbetalipoproteinemia, the most common cause for this form is the presence of ApoE E2/E2 genotype. It is due to cholesterol-rich VLDL (β-VLDL). Prevalence is 0.02% of the population.

Hyperlipoproteinemia type IV

This form is due to high triglycerides. It is also known as hypertriglyceridemia (or pure hypertriglyceridemia). Prevalence is 1% of the population.

Hyperlipoproteinemia type V

This type is very similar to type I, but with high VLDL in addition to chylomicrons.

Unclassified forms

Non-classified forms are extremely rare:

References

External links

! Hyperlipoproteinemia
! OMIM
! GPnotebook
! MebMD
! Others

! Type I
| OMIM [238600]
| >
| .
| [MeritCare]

! Type IIa
| rowspan=2 | OMIM [144400]
| >
| .
| rowspan=2 | [Merck]

! Type IIb
| >

| .

! Type III
| .
| GPnotebook [630849560]
| [WebMD]
| [Yahoo]

! Type IV
| OMIM [144600]
| >
| [WebMD]
| [Yahoo]

! Type V
| OMIM [144600]
| >
| .
| .

 

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