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Carnitine Deficiency Syndrome is a rare metabolic disorder that may be inherited in some cases, or occur as a result of other metabolic disorders. Carnitine functions in the body as a carrier of fatty acids to the energy centers in muscles (mitochondria). A deficiency of carnitine, normally produced by the liver and kidneys, can result in extreme muscle weakness and other related symptoms.
There may be two types of Carnitine Deficiency: Myopathic Carnitine Deficiency (affecting muscles) and Systemic Carnitine Deficiency (affecting the entire body).
Muscle weakness is the primary symptom of Myopathic Carnitine Deficiency Syndrome. Shortages and/or interrupted supplies of energy to muscles may result in the destruction of muscle tissue. Oxygen-carrying protein (myoglobulin) may also be lost and secreted in the urine (rhabdomyolyis).
Systemic Carnitine Deficiency Syndrome differs from Myopathic Carnitine Deficiency because low levels of carnitine are found in tissues other than muscles, including blood and/or urine. There may also be a deficiency of carnitine in the central nervous system, liver, and/or heart. Symptoms may include loss of brain tissue (degenerative encephalopathy), episodes of vomiting, confusion, and/or stupor that progresses to coma.
Carnitine Deficiency Syndrome may also be associated with low blood sugar (hypoglycemia). Damage to the heart muscle may result in chronic heart disease (cardiomyopathy).
The Carnitine Deficiency Syndromes may be classified as primary or secondary. When a person is thought to have no other underlying disease that could cause low levels of carnitine, then the deficiency is termed "primary." When the deficiency is caused by another underlying disorder, then it is said to be "secondary."
In some cases of this disorder, total carnitine levels may be normal but are nonetheless insufficient to meet metabolic needs because of the presence of another associated disorder.
Primary Carnitine Deficiency Syndrome is thought to be inherited as an autosomal recessive genetic trait. Human traits, including the classic genetic diseases, are the product of the interaction of two genes, one received from the father and one from the mother. In recessive disorders, the condition does not appear unless a person inherits the same defective gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk of transmitting the disease to the children of a couple, both of whom are carriers for a recessive disorder, is 25 percent. Fifty percent of their children risk being carriers of the disease, but generally will not show symptoms of the disorder. Twenty-five percent of their children may receive both normal genes, one from each parent, and will be genetically normal (for that particular trait). The risk is the same for each pregnancy.
Secondary Carnitine Deficiency usually occurs as a symptom of metabolic disorders such as organic acidemias. In rare cases, Carnitine Deficiency may also occur when there is severe liver disease or kidney (renal tubular) malfunction.
Primary Carnitine Deficiency Syndrome is a rare disorder that affects males and females in equal numbers. There are only a few hundred patients in the United States with Primary Carnitine Deficiency. People who have any of the organic acidemias, mitochondrial disorders, severe liver disease, and/or renal tubular dysfunction may be at risk of developing Secondary Carnitine Deficiency.
Symptoms of the following disorders can be similar to those of Carnitine Deficiency Syndrome. Comparisons may be useful for a differential diagnosis:
Isovaleric Acidemia is a rare inherited metabolic disorder (organic acidemia) of infancy characterized by attacks of vomiting, lack of appetite, and fatigue. Infants with this disorder become progressively weak and often have abnormally low body temperatures (hypothermia). A strong offensive body odor is also associated with this disorder. (For more information on this disorder, choose "Isovaleric Acidemia" as your search term in the Rare Disease Database.)
Propionic Acidemia is another form of organic acidemia that occurs in infancy. It is caused by a deficiency of the enzyme propionyl-CoA carboxylase (PCC). The initial symptoms of Propionic Acidemia include failure to thrive, vomiting, and extreme fatigue. Children who are very ill may have a better response to L-carnitine administered intravenously.
Mitochondrial Cytopathies are a group of disorders that affect the ability of the body's cells to turn food into energy. Without sufficient energy, cells may be unable to function properly. Furthermore, incompletely metabolized food byproducts may accumulate and act as poisons within the body. These disorders are caused by a malfunction in one of five enzymes, referred to as complexes I, II, III, IV, and V. They may involve only one or several organs or systems, including the brain, nerves, muscles, and heart, and their effects range greatly in severity.
The orphan drug L-carnitine (Carnitor) is available in tablet and liquid form. It is manufactured by Sigma Tau Pharmaceuticals. For more information on this drug, contact:
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Coenzyme Q10, a vitamin-like substance, is being studied as a possible treatment for mitochondrial disorders. More studies are needed to determine the long-term safety and effectiveness of this treatment.
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Online Mendelian Inheritance in Man (OMIM). Victor A. McKusick, Editor; Johns Hopkins University, Last Edit Date 5/25/99, Entry Number 212140.
Report last updated: 2009/04/08 00:00:00 GMT+0