Asthma is a heterogeneous group of conditions that result in recurrent, reversible bronchial obstruction. Although the disease can start at any age, the fi rst symptoms occur during childhood in most cases. Asthma has a strong genetic component, and genome-wide association studies have identifi ed variations in several genes that slightly increase the risk of disease. Asthma is often associated with increased susceptibility to infection with rhinoviruses and with changes in the composition of microbial communities colonising the airways, but whether these changes are a cause or consequence of the disease is unknown. There is currently no proven prevention strategy; however, the fi nding that exposure to microbial products in early life, particularly in farming environments, seems to be protective against asthma off ers hope that surrogates of such exposure could be used to prevent the disease. Genetic and immunological studies point to defective responses of lung resident cells, especially those associated with the mucosal epithelium, as crucial elements in the pathogenesis of asthma. Inhaled corticosteroids continue to be the mainstay for the treatment of mild and moderate asthma, but limited adherence to daily inhaled medication is a major obstacle to the success of such therapy. Severe asthma that is refractory to usual treatment continues to be a challenge, but new biological therapies, such as humanised antibodies against IgE, interleukin 5, and interleukin 13, off er hope to improve the quality of life and long-term prognosis of severe asthmatics with specifi c molecular phenotypes.
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