Section 12. Disorders of Nutrition and Metabolism

Chapter 157. Disorders of Cholesterol

Topics: Introduction | Hyperlipoproteinemia | Hypolipoproteinemia

Hypolipoproteinemia

Hypolipoproteinemia is abnormally low levels of lipids in the blood.

Having low lipid levels rarely causes a problem, but it may indicate the presence of another disorder. For example, a low cholesterol level may indicate an overactive thyroid gland (hyperthyroidism), anemia, undernutrition, cancer, or impaired absorption of foods from the digestive tract (malabsorption). Therefore, doctors may suggest further evaluation when the total cholesterol is less than 120 mg/dL. A few rare hereditary disorders, such as abetalipoproteinemia and hypoalphalipoproteinemia, result in lipid levels low enough to have serious consequences.

In abetalipoproteinemia, a rare disorder, no LDL cholesterol is present, and the body cannot make chylomicrons. As a result, the absorption of fat and fat-soluble vitamins is greatly impaired. Bowel movements contain excess fat (a condition called steatorrhea). Red blood cells are misshapen. The retina of the eye degenerates, causing blindness (this condition is similar to retinitis pigmentosa). The central nervous system may be damaged, resulting in loss of coordination (ataxia). Although abetalipoproteinemia cannot be cured, taking massive doses of vitamin E may delay or slow the damage to the central nervous system.

In hypobetalipoproteinemia, the LDL cholesterol level is very low. Usually, there are no symptoms and no treatment is required. In the most severe form of hypobetalipoproteinemia, almost no LDL cholesterol is present. The symptoms are similar to those of abetalipoproteinemia.

In hypoalphalipoproteinemia, the HDL cholesterol level is low. A low HDL cholesterol level is often inherited. Obesity, physical inactivity, cigarette smoking, diabetes, or kidney disorders (such as nephrotic syndrome) may contribute to a low HDL cholesterol level. Drugs such as beta-blockers and anabolic steroids can lower the HDL cholesterol level. Having a low HDL cholesterol level increases the risk of atherosclerosis (see Section 3, Chapter 32). Therefore, lifestyle changes to eliminate conditions that lower the HDL cholesterol level are advised when applicable: losing weight, increasing physical activity, and stopping smoking. Some lipid-lowering drugs increase the HDL cholesterol level and may be used in people who also have high LDL cholesterol or triglyceride levels.