How Big a Role does Genetics Play in the Development of Asthma?

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What Happens During an Asthma Attack?

Asthma attacks can be triggered by a wide range of substances: animal hair, skin, and feathers; insects, such as cockroaches and dust mites; pollen, dust, mold, and smoke; air pollution; colds and airway infections; and even exercise.

During an asthma attack, the muscles in the airway begin to contract, which causes the airway to become narrower. The airway also begins to swell, which further narrows the passage. Finally, the production of mucus the airway produces constricts it even further.

This is fairly similar to what happens during an allergic reaction, and, in fact, asthma and allergic reactions are mediated by the same arm of the immune response system (based on the antibody called IgE, which has few other functions apart from mediating allergies).

Genetic Research has Produced Conflicting Results

Recent research on genetic causes of asthma has uncovered some interesting and important information about the possible genetic mechanisms which influence the development of the condition.

In April 2008, researchers from the Yale School of Medicine and the University of Chicago reported they had discovered that a gene which was previously known only as a genetic marker for asthma could also—in cases where the gene was mutated—be linked to the cause of the disease.

Prior to the publication of the study in the New England Journal of Medicine, it had been discovered that the gene was associated with codes for a protein called YKL-40. Blood levels of the protein are elevated in people with asthma.

In the April 2008 study, the researchers found that a mutation in YKL-40 was associated with increased levels of the protein in the blood, and also with both asthma and impaired lung function.

It is important to note, though, that while there is definitely a strong correlation between genetics and asthma, it’s not the whole story. In a twin study carried out in the 1990s, researchers Sarafino and Goldfedder showed that environmental factors are also important.

In that study, the researchers examined pairs of identical and non-identical twins, with some interesting results. In 59% of the identical twins, both twins had asthma; however, both twins had asthma in just 24% of the non-identical twin pairs.

Essentially, the experiment showed that asthma is both a genetic and an environmental condition. If it were solely genetic, it would be much more common for both twins in an identical pair to develop asthma—and if it were solely environmental, there should be little difference in the incidence rate between identical and non-identical twins.

So How Important is Genetics?

Research on the genetic basis of asthma is still not conclusive. Genetics clearly plays an important role, but there are other factors at work. It is likely that while asthma is not solely an inherited condition, the tendency to develop asthma is inheritable.

Finally, it’s likely that when asthma “runs in the family” genetics are more influential than environmental factors in determining whether an individual in that family develops asthma. On the other hand, if asthma doesn’t run in the family, the opposite is more likely to be true, and environmental factors play a more influential role.