Disorders of lipid metabolism

Disorders of lipid metabolism often manifest as dyslipidemia. Elevated plasma levels of some lipoproteins are characteristic. The frequency of dyslipidemia in the population is around 2–3%, but according to the latest diagnostic criteria, it affects more than half of the population. It is a significant risk factor for coronary heart disease along with smoking and hypertension. Treatment of dyslipidemia significantly reduces the risk of cardiovascular disease.



Disorders of lipid metabolism may involve either lipid transport (hyperlipoproteinemia, hypolipoproteinemia, dyslipoproteinemia) or lipid storage on cells (sphingolipidosis). In addition to primary hyperlipoproteinemias arising from genetic disorders (inherited metabolic disorders), hyperlipoproteinemias can also be secondary to other diseases (caused by the diseases or associated with them) such as diabetes, hepatopathy, renal failure, alcoholism, and endocrinopathy. Atherosclerosis and obesity have been associated with some hyperlipoproteinemias.


 * Hyperlipidemia: the increase in plasma concentrations of specific lipids (TC, TAG, or a combination of both).
 * Hyperlipoproteinemia: an increase in one or more lipoprotein classes (classification according to Fredrickson, or WHO).


 * Dyslipidemia: this refers to all metabolic abnormalities of lipid metabolism (↓ HDL alone or in combination with ↑ other lipids).

Classification
According to the European Society for Atherosclerosis into 3 groups:
 * Isolated hypercholesterolemia (manifested mainly by xanthelasmas and tendon and tuberous xanthomas)
 * Isolated hypertriglyceridemia (manifested mainly by eruptive xanthomas and hepatomegaly)
 * Combined hyperlipidemia

Etiology
The most common are genetically conditioned primary dyslipidemias (DLP):
 * Familial hypercholesterolemia: the most severe primary DLP (risk of premature coronary heart disease). It is caused by a defect in the LDL receptor gene, leading to severe impairment in the removal of LDL from the blood; thus, it accumulates.
 * Familial combined hyperlipoproteinemia: the most common primary DLP
 * Familial defect apo-B-100 (ligand for LDL receptor)
 * Familial hypertriacylglycerolemia.

Secondary dyslipidemias may have a combined etiology of:
 * A lipid-rich diet (associated with increased plasma levels of total cholesterol) rich in oligosaccharides (associated with increased plasma levels of TAGs).
 * Hypothyroidism, Cushing's syndrome, and diabetes mellitus
 * Side effects of corticosteroids, estrogens, thiazide diuretics
 * Nephrotic syndrome
 * Alcoholism
 * Cholestasis
 * Anorexia nervosa, bulimia
 * Smoking, obesity, low physical activity (↓ HDL)

Clinical examination

 * Genealogy
 * Determination of BMI, waist circumference, and blood pressure
 * Examination of peripheral arteries (pulsations, murmurs)
 * The presence of arcus lipoides corneae, xanthelasmas, and xanthomas

Laboratory tests

 * Determination of plasma values of TC, TAG, and HDL
 * LDL calculation (or direct determination): LDL-cholesterol = total cholesterol – (HDL-cholesterol + TAG/2,2)
 * Glycemia, glycated Hb

Reference values

 * Total cholesterol < 5,0 mmol/L
 * LDL-cholesterol < 3,0 mmol/L
 * Triglycerides < 1,7 mmol/L
 * HDL-cholesterol > 1,0 mmol/L for men, > 1,2 mmol/L for women
 * Atherogenic index (= total cholesterol/HDL-cholesterol) < 5

Related articles

 * Disorders of lipid metabolism (detailed)
 * Dyslipidemia
 * Lipoproteins
 * Lipoproteins (clinic)
 * Treatment of hyperlipidemia
 * Atherosclerosis
 * Obesity