What Causes Asthma?

One of the more frequent questions my patients ask me concerns the relative risk of their child developing allergies or asthma. In previous Doctors' Views, I have raised issues relating the environment to the development of allergies or asthma. However, both a genetic predisposition and environmental/lifestyle factors are necessary for these conditions to develop.

The incidence of asthma has risen dramatically in the past 20 years, a period 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 link in asthma has long been suspected primarily due to "clustering" of cases within families and in identical twins. This does not prove a genetic cause, since it may also reflect shared environmental exposures. Several studies conclude that heredity increases your chances of developing asthma, particularly if allergies or other allergic conditions are present. Moreover, you may pass this tendency to asthma to the next generation. So, what are the chances that your 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 one parent who has asthma are three to six times more likely to develop the condition, and children with two parents with asthma are 10 times more at risk. Certainly, identical twins are more likely to share allergies and asthma than are nonidentical (fraternal) twins. Asthma may skip a generation or surface in other branches of your family. Inheriting the asthma gene does not necessarily mean that you will definitely develop asthma.

The genetic material that you were born with, the amount of environmental asthma-promoting factors in your environment, and your lifestyle can all conspire to put you more or less at risk for developing asthma. As such, your genetic makeup is only one piece of the puzzle.