Asthma is a respiratory disorder characterized by an inflammation of the airways with recurrent episodes of respiratory distress. These episodes, known as asthmatic crises, are caused by irritation of the inflamed airways. In allergic asthma, crises occur when allergens are inhaled that cause a hypersensitivity reaction. The most frequent allergens are plant pollens, house dust, animal dander and molds (filamentous fungi). The immune response causes asthma symptoms. In almost 90% of children and 50% of adults with asthma, the disease is classified as allergic asthma.
A distinctive feature of asthma is bronchial hyperreactivity, which means that the airways are especially sensitive to irritants and respond excessively. Due to hyperreactivity in people with allergic asthma, crises can be caused by conditions or irritants other than allergens, such as physical activity, respiratory infections or exposure to tobacco smoke.
An asthma crisis is characterized by bronchoconstriction, which narrows the airways and causes respiratory distress. In addition, the immune response can cause inflammation of the airways and overproduction of mucus. During a crisis, the affected person may suffer chest tightness, wheezing, respiratory distress and cough. Over time, the muscles surrounding the airways may hypertrophy, narrowing the airways further. Some people with allergic asthma have another allergic disorder, such as allergic rhinitis or food allergies.
Occasionally, asthma is part of a set of allergic disorders. The development of these alterations usually follows a pattern; it starts with atopic dermatitis, followed by food allergies, then hay fever, and finally asthma. However, not all individuals with asthma progress through this sequence, just as not all individuals with a single allergic disease will develop others.
The cause of allergic asthma is complex. It is likely that a combination of multiple genetic and environmental factors contribute to the development of the disease. It is considered that certain genes are involved, since having a family member with allergic asthma or another allergic disease increases the risk of developing asthma in people. More than 100 genes could be associated with allergic asthma, but each gene seems to be a predisposing factor in one or some populations. Many of these associated genes are involved in the body's immune response. Other genes play a role in lung and airway function.
There is evidence that an unbalanced immune response underlies allergic asthma. While there is normally a balance between type 1 (Th1 o) and type 2 (Th2 o) of the body's immune responses, many individuals with allergic asthma have a predominance of type 2. Type 2 responses give rise to coding of IgE antibodies and the generation of other factors that predispose to bronchial hyperreactivity. Normally, the body encodes IgE antibodies in response to foreign invaders, in particular helminth parasites. For unknown reasons, in individuals prone to asthma, the body reacts to an allergen as if it were harmful, through the coding of specific IgE antibodies. In subsequent allergen exposures, IgE antibodies recognize them and stimulate the immune response, leading to bronchoconstriction, inflammation of the airways and mucus production. Not all people with a variation in one of the genes associated with allergic asthma develop the disorder. Exposure to certain environmental factors also contributes to its development. It is considered that these exposures trigger epigenetic changes in DNA. Epigenetic changes modify the DNA without changing its sequence, being able to affect the activity of the gene and regulate the coding of proteins, thus influencing the development of allergies in susceptible individuals.
Allergic asthma can be transmitted from generation to generation in families, but the inheritance pattern is unknown. People with mutations in one or more of the associated genes have an increased risk of allergic asthma, but not the disease itself. Because allergic asthma is a complex disorder influenced by genetic and environmental factors, not all people with a mutation in a gene associated with asthma will develop the disease.
Tests carried out in IVAMI: due to the doubts that exist in the genetic contribution to the development of allergic asthma, in IVAMI we are not currently detecting mutations associated with allergic asthma.