Disorders of lipid metabolism

Disorders of lipid metabolism, also dyslipidemia, formerly hyperlipidemia are metabolic diseases. Elevated plasma levels of some lipoproteins are characteristic. The frequency of dyslipidemias in the population is around 2–3 %, but according to the latest diagnostic criteria, they affect more than half of the population. It is a significant risk factor for coronary heart disease along with smoking and hypertension. Treatment of dyslipidemia then significantly reduces the incidence of cardiovascular disease.



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


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


 * Dyslipidemia – more recently 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 xanthelasms, tendon and tuberous xanthomas);
 * isolated hypertriglyceridemia (manifested mainly by eruptive xanthomas and hepatomegaly);
 * mixed hyperlipidemia

Etiology
The most common are genetically conditioned primary dyslipidemias (DLP):
 *  familial hypercholersterolemia – the most severe primary DLP (risk of premature coronary heart disease), defect in the LDL- receptor gene (severe removal of LDL from the blood);
 * 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:
 * fatty diet (rather increases cholesterol), rich in oligosaccharides (increases TAG);
 * hypothyroidism, Cushin's syndrome, Diabetes mellitus;
 * side effects with 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, blood pressure;
 * examination of peripheral arteries (pulsations, murmurs);
 * the presence of arcus lipoides corneae, xanthelasms and xanthomas.

Laboratory tests

 * direct plasma values of TC (total cholesterol), TAG, HDL;
 * LDL computation (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)
 * Hypolipidemic treatment
 * Atherosclerosis
 * Obesity