Very long-chain acyl-coenzyme A dehydrogenase (VLCAD) deficiency is a condition in which the body does not properly convert certain types of fat into energy, particularly during periods of fasting, illness, or exercise.
There are three different forms of VLCAD deficiency, ranging from severe symptoms present at birth to very mild symptoms that develop during adulthood:
Severe Early-Onset Form
Infants with the most severe form of VLCAD deficiency develop symptoms within the first few months of life. It causes a thickening of the heart muscle or other weakness of the heart (cardiomyopathy) which impairs its function. It can also cause an abnormal heart rhythm and/or fluid around the heart. These symptoms can be fatal if not recognized and treated promptly. The disease can also cause poor muscle tone, lack of energy, an enlarged liver, and periods of low blood sugar (hypoglycemia).
Hepatic or Hypoketotic Hypoglycemic Form
This form of VLCAD deficiency often appears in early childhood, and is similar to the more severe version except that it does not affect the heart. People with the hepatic or hypoketotic form typically have low blood sugar and an enlarged liver.
Late-Onset Episodic Myopathic Form
People who have the late-onset form of VLCAD deficiency, which is thought to be the most common form of the disease, typically experience mild symptoms beginning in adolesence or adulthood, and some do not experience any symptoms at all. This form also does not normally affect the heart and may not cause low blood sugar. People with this form of the disease may experience occasional periods of muscle cramps or muscle pain and rhabdomyolysis, which is when the body breaks down muscle fibers, releasing a protein into the bloodstream that can damage the kidneys and turn one's urine a dark brown or red color. These symptoms may occur more frequently after exercise.
All three types of VLCAD deficiency are caused by an error in the production of an enzyme called very long-chain acyl-coenzyme A dehydrogenase. This enzyme breaks down a type of fat known as very long-chain fatty acids and converts it into energy. People with VLCAD deficiency do not have enough of this enzyme, and as a result, the fats are not converted into energy, leaving the person with low blood sugar (hypoglycemia) and feelings of weakness or tiredness. In addition, a buildup of very long-chain fatty acids in the body can damage the heart, liver, and muscles, causing the additional symptoms of the disease.
VLCAD deficiency affects 1 in every 40,000 to 120,000 people.
People with VLCAD deficiency may be prescribed a special diet. In severe, early-onset cases of the disease, this is often includes intravenous glucose and/or a low-fat formula designed with types of fat the person is better able to digest. With early and active medical care, any heart problems associated with the severe form of the disease can typically be reversed.
Adults who experience episodes of rhabdomyolysis can be treated through adequate hydration and efforts to lower the acidity of the urine to protect the kidneys.
People with VLCAD deficiency should avoid long periods without eating, dehydration, and a high fat diet.
With early diagnosis and treatment, the prognosis for a person with VLCAD deficiency is very good. Many are able to live without symptoms and have normal physical and mental development. If the more severe cases of VLCAD deficiency are not detected and treated early, however, the disease can be fatal.
In milder cases of adult-onset VLCAD deficiency, many people remain symptom-free for life even without treatment.
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Explanations of an extensive number of genetic diseases written by the U.S. government's National Institutes of Health.