Low level of AAT enzyme raises emphysema risk


December 08, 1992|By Dr. Simeon Margolis | Dr. Simeon Margolis,Contributing Writer

My doctor has urged me to stop smoking because low levels of some enzyme in my blood show that I am at high risk to develop lung disease. Could you help me to understand the problem?

Undoubtedly your doctor has found that you have low levels of the enzyme alpha-antitrypsin (AAT) in your blood. A deficiency of AAT is a fairly common inherited disorder associated with an increased tendency to develop emphysema, a chronic lung disease that leads to increasing shortness of breath as it progresses. Emphysema is caused by destruction of the small air sacs and loss of elasticity in the lungs.

As a result, the small air passages tend to collapse and obstruct the flow of air, especially when breathing out.

Although the cause of emphysema is not fully understood, it is believed that enzymes that break down proteins damage the elastic tissue in the lungs by destroying its major protein, elastin.

White blood cells in the lower respiratory tract release the enzyme that breaks down elastin, called elastase, and its destructive action is normally blocked by AAT.

Individuals with AAT deficiency have a lower level of AAT that leaves the elastin in air sacs unprotected from damage by elastin. And continued loss of elastic tissue over many years eventually leads to emphysema.

AAT prepared from human blood is available by prescription. Repeated intravenous infusions of AAT can raise its blood level and may slow the progression of emphysema in people with some forms of AAT deficiency. But no long-term studies have been performed to show that AAT administration delays the development of emphysema in individuals who inherit low levels of AAT.

Cigarette smoking accelerates the onset of emphysema in everyone, but especially in those with an inherited AAT deficiency. The most important thing you can do to reduce your risk for emphysema is to stop smoking cigarettes.

Dr. Margolis is professor of medicine and biological chemistry at the Johns Hopkins School of Medicine and associate dean for faculty affairs at the school.

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