title: Genetics and epidemiology: asthma and infection.
abstract: OBJECTIVE
  This review will consider how recent epidemiological studies have helped reveal the role of respiratory infection in asthma inception early in life. We will also review the importance of respiratory infections and exacerbations of asthma and will discuss genetic factors controlling host immune responses to respiratory infection and the influence these may exert on asthma pathogenesis.
  
  
  RESULTS
  Birth cohort studies have demonstrated bidirectional relationships between early life severe respiratory infections and asthma development; however, whether there is a clear causal role for severe respiratory infection early in life leading directly to asthma development remains unknown. The role of rhinovirus infection in asthma exacerbations has been investigated experimentally, with asthmatic patients exhibiting greater clinical illness severity, which was related to increased virus load and lower airways inflammation. Polymorphisms in genes involved in innate, antiviral and Th1 and Th2 immune responses have been linked to asthma as well as to early life severe respiratory infections, suggesting that host factors are likely to play an important role in their association.
  
  
  CONCLUSIONS
  Early in life, such genetic factors contribute to the risk of severe lower respiratory tract viral infection as well as later development of wheezing illness and asthma. Respiratory viruses are also the most frequent cause of asthma exacerbations at all ages.
authors: Department of Respiratory Medicine, National Heart and Lung Institute, Imperial College London, UK.
authors: Nathan W
authors: NW
authors: Bartlett
authors: Gary R
authors: GR
authors: McLean
authors: Yoon-Seok
authors: YS
authors: Chang
authors: Sebastian L
authors: SL
authors: Johnston
mesh_terms: D017668:Age of Onset; D001249:Asthma / Q000150:complications / Q000453:epidemiology / Q000235:genetics* / Q000503:physiopathology; D020022:Genetic Predisposition to Disease; D006801:Humans; D007109:Immunity / Q000235:genetics; D015994:Incidence; D020412:Multifactorial Inheritance; D010850:Picornaviridae Infections / Q000150:complications / Q000453:epidemiology / Q000235:genetics* / Q000503:physiopathology; D011110:Polymorphism, Genetic; D012141:Respiratory Tract Infections / Q000150:complications / Q000453:epidemiology / Q000235:genetics* / Q000503:physiopathology; D012229:Rhinovirus / Q000276:immunology* / Q000472:pathogenicity; D012307:Risk Factors