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Asthma phenotypes in childhood: lessons from an epidemiological approach

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Abstract

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.

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COHORT STUDIES AND ASTHMA FOLLOW-UP FROM CHILDHOOD TO ADULTHOOD

The recent publication of adequately powered, well-designed longitudinal studies with follow-up starting during the first years of life has produced a remarkable change in our understanding of asthma, its beginnings, its clinical expression and its evolution.

A recent study by Sears et al.7 evaluated a cohort from Dunedin, New Zealand, followed from 9 to 26 years of age with questionnaires, pulmonary function tests, bronchial challenge testing and allergy testing. The authors defined wheezing as

ASTHMA PHENOTYPES

These wheezing syndromes are characterised by the persistence or remittance of wheeze and wheeze-associated symptoms from childhood to adulthood. We have proposed that three can be defined based on specific characteristics: transient early wheezers (wheezing up to 3–5 years of age but not thereafter), non-atopic wheezing and IgE-mediated wheezing/asthma (Fig. 3).

PRACTICE POINTS

  • Asthma is a heterogeneous disease with well recognized wheeze phenotypes in childhood.

  • Wheezing in the first years of life is not associated with atopy, and is thus called transient wheezing. It is known to be associated with diminished lung function.

  • A group of asthmatic children who are still symptomatic with episodes of wheezing up to adolescence do present a milder form of disease, associated with RSV and not with atopy, i.e., non-atopic wheezers.

  • Persistent wheezing, the ‘classic’ asthma is

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