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Asthma, Eczema And Rhinitis: A Deleterious Strong Heritage

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Over the past three decades, the prevalence of childhood asthma has increased substantially. It has been hypothesised that environmental risk factors, such as parental smoking, number of siblings, and air pollution, are responsible for this increase.

A study of the Dutch Twin Registry examined both environmental and genetic risk factors in susceptibility to asthma, eczema, and rhinitis in a large group of children.The study collected data through parental report on about 16,000 5-year-old Dutch twins born between 1986 and 1998. Parents were asked whether a physician ever diagnosed their children with asthma, eczema, or rhinitis.The researchers find an almost doubling of the asthma rate in children born in the late nineties compared to children born in the eighties. Across birth cohorts, the rate of eczema and rhinitis remained stable.The main result of the study, however, is that asthma, eczema, and rhinitis are highly heritable disorders. In addition, the results suggest that environmental factors, shared by family members, are not important as main effects. Thus, the fact that twins grow up in the same house and experience the same environmental risk factors, does not contribute by itself to the variance in susceptibility to asthma.This lack of evidence for shared environmental factors as main effects can be explained by gene-environmental interactions. It is likely that environmental risk factors trigger asthma only in persons with larger genetic susceptibility for allergic and asthmatic diseases.Siblings and dizygotic twins share only 50% of their segregating genes. One child can thus be genetically susceptible and his or her sibling not. If the influence of the home environmental risk factors depends on genotype, as suggested by these results, genotype-environment explains the large heritability for asthma and related disorders.(Source: European Respiratory Journal : Vrije Universiteit, Amsterdam : March 2007.)

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Posted On: 8 March, 2007
Modified On: 16 September, 2014

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