A study of Chinese adolescents living in mainland China, Hong Kong and Canada suggests that asthma may be influenced by environmental factors as well as genetics (http://www.cmaj.ca/press/pg1133.pdf).
Researchers based in Canada and China looked at 13,223 school children aged 13-14 from Vancouver, Guangzhou, Beijing and Hong Kong, of whom 10,924 were included in the analysis. Asthma symptoms in Chinese adolescents were lowest among those living in mainland China, higher for those in Hong Kong or immigrating to Canada, and highest among those born in Canada.
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Journal
Canadian Medical Association Journal