Asthma is a condition that likely results from complex interactions between multiple genetic and environmental influences. Studies of twins and of families of asthmatic individuals have shown that asthma occurs in a pattern consistent with heritable factors [1-3]. There are clearly components of the asthma phenotype that appear strongly heritable, although these inherited components do not follow the simple Mendelian pattern that is seen in monogenic disorders such as cystic fibrosis, and the specific genes responsible for these inherited components have yet to be identified. (See "Basic principles of genetic disease".)
The genetics of asthma will be reviewed here; epidemiology and risk factors are discussed separately. (See "Epidemiology of asthma" and "Risk factors for asthma".)
ISSUES IN STUDYING ASTHMA GENETICS
Human and animal data currently suggest that the syndrome of asthma is likely transmitted by multiple genes. In addition, different genes in different individuals may lead to the same phenotype (locus heterogeneity), and multiple genes acting in the same individual (oligogenic or polygenic inheritance) may culminate in expression of the asthma phenotype .
Some genes may influence the development of asthma, while others modify asthma severity or the patient's response to therapy. Finally, interactions between genetic factors and environmental influences provide another layer of complexity.
Exploration of the genetics of asthma has also been hampered by the fact that there is no "gold standard" diagnostic test for asthma, and the clinical diagnosis is inconsistently applied. To circumvent these issues, investigators have studied the distribution of asthma-related traits, including bronchial hyperresponsiveness and measures of atopy (eg, total serum IgE levels, skin test reactivity), in addition to the presence or absence of an asthma diagnosis [5,6]. (See "Diagnosis of asthma in adolescents and adults".)