Asthma phenotypes in childhood: lessons from an epidemiological approach.

Asthma is a heterogenous disease with variable signs and symptoms among patients. It also presents significant individual variability over time. Recently, some important population-based studies that followed children from birth or from early childhood into adulthood have shed new light on how we understand this syndrome. Three phenotypes have been identified in children with asthma: transient wheezing, non-atopic wheezing of the toddler and pre-school-aged child and IgE-mediated wheezing. Transient wheezing is associated with symptoms that are limited to the first 3-5 years of life, decreased lung function, maternal smoking during pregnancy and exposure to other siblings or children at daycare centres. There is no association between transient wheezing and family history of asthma or allergic sensitisation. Children wheezing with respiratory syncytial virus in the first years of life are more likely to be wheezing up to 13 years of age; this is independent of atopy (non-atopic wheezers) and is not related to atopic sensitisation. Wheezing associated with evidence of allergic sensitisation has been identified as the 'classic' asthma phenotype. Early allergic sensitisation is a major risk factor for persistent asthma.