PURPOSE OF THE STUDY.
The goal of this study was to identify asthma phenotypes in a prospective birth cohort study based on age of onset and clinical evolution and to characterize their respective associated risk factors.
The study population included members of MACS (Melbourne Atopy Cohort Study), a birth cohort at high risk for allergy consisting of 620 children who were followed up prospectively at defined time points during the first 7 years of life. An additional evaluation was conducted at 12 years of age.
Latent class analysis was used to categorize asthma phenotypes in the context of wheeze patterns between 4 weeks and 7 years of age. Relative contributions of known clinical and demographic characteristics to the defined clusters of wheeze phenotypes were also evaluated in a logistic regression analysis.
The study identified 5 distinct wheeze phenotypes: never/infrequent, early transient (appeared in first 12 months and resolved by 3 years), early persistent (wheezing appeared in the first 6 months), intermediate onset (wheezing onset at ∼18 months), and late onset (occurred at ∼4 years); the latter 3 groups were associated with increased risk of current wheeze at 12 years. Consistent with previous observations, an increased propensity to childhood wheeze was noted with lower respiratory tract infection before 1 year. However, this risk was abrogated when adjusted for aeroallergen and food sensitization, and the strength of this association declined over time, becoming nonsignificant in the late-onset group. The study found protective effects of dog exposure at baseline and first-born status against intermediate-onset wheezing. Breastfeeding for >3 months reduced the risk of both early transient and late-onset wheezing. Parental smoking was a risk factor associated with late-onset wheeze.
The study confirmed the contributory role of various early-life exposures to the generation of distinct childhood wheeze phenotypes in a birth cohort at high risk of allergy.
The heterogeneity of childhood asthma is being increasingly recognized, as determined by using multiple environmental and biological factors. The study reinforced known clinical and demographic associations with early-life wheeze. However, the definition of wheeze phenotypes was largely based on the empirical categorization of the investigators. In addition, further information regarding disease course and outcomes was not available, and future longitudinal studies are necessary to determine the clinical relevance of the identified phenotypes in terms of stability over time and also in predicting severity and treatment response.
- Copyright © 2014 by the American Academy of Pediatrics