Definition of Asthma

Asthma: A common disorder in which chronic inflammation of the bronchial tubes (bronchi) makes them swell, narrowing the airways. Asthma involves only the bronchial tubes and does not affect the air sacs (alveoli) or the lung tissue (the parenchyma of the lung) itself.

Airway narrowing in asthma is due to three major processes acting on the bronchi: inflammation (see above), spasm (bronchospasm), and hyperreactivity (over-reaction of the bronchi to factors that can precipitate asthma).

The incidence of asthma has risen dramatically in the past 20 years, a period far too short to reflect any significant changes in the gene pool. This supports the important role that environmental influences (allergy, infection, lifestyle, and diet) have on the development of asthma.

A genetic role in asthma has long been suspected, primarily due to the clustering of cases within families and the concordance for asthma in identical twins. Several studies conclude that heredity increases ones chances of developing asthma, particularly if allergies or other allergic conditions are present. Moreover, one may pass this tendency to asthma to the next generation. So, what are the chances that a child will develop asthma?

• 6.5% of families in which neither parent has asthma have a child with asthma.
• 28% of families in which one parent has asthma have a child with asthma.
• 63% of families in which both parents have asthma have at least one child with asthma.

In other words, when compared with children whose parents do not have asthma, children with 1 parent who has asthma are 3-6 times more likely to develop the condition and children with 2 parents with asthma are 10 times more at risk. Certainly, identical twins are more likely to share allergies and asthma than are non-identical (fraternal) twins.

A hunt lasting a decade and spanning two continents led in 2004 to the finding of two asthma genes on chromosome 7p. A candidate gene was found encoding a G protein-coupled receptor named GPRA (G protein-coupled receptor for asthma susceptibility). GPRA appears involved in the susceptibility to allergy and asthma.

Inheriting genes for asthma does not necessarily mean that a person will definitely develop asthma. The genes make for susceptibility. The susceptibility genes together with the asthma-promoting factors in your environment, and your lifestyle can all conspire to put you at risk for developing asthma. As such, your genetic make-up is only one piece of the puzzle.

Many environmental factors are known to precipitate attacks of asthma. These factors are all either allergens or irritants. Allergic factors play a role in many, but by no means every, case of asthma.

Signs and symptoms include shortness of breath, chest tightness, cough and wheezing. The diagnosis is based on these features (without wheezing, it is not asthma) and is confirmed with breathing tests. Chest X-rays are usually normal in people with asthma.

As a rule, the bronchial narrowing characteristic of asthma can be partially or completely prevented or reversed with proper treatment. Avoiding precipitating factors is important in managing asthma.

Source: MedTerms™ Medical Dictionary
http://www.medterms.com/script/main/art.asp?articlekey=2373
Last Editorial Review: 4/8/2004