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Dimensions of Respiratory Symptoms in Preschool Children

Population-based Birth Cohort Study

¹ Respiratory Research Group, ² Divisions of Psychiatry and ³ Biostatistics, Health Methodology Research Group, University of Manchester, Manchester, United Kingdom

Correspondence and requests for reprints should be addressed to Dr. Jaclyn A. Smith, M.D., Ph.D., University of Manchester, ERC Building, Second Floor, Wythenshawe Hospital, Manchester M23 9LT, UK. E-mail: jacky.smith{at}manchester.ac.uk

Rationale: A focus on distinctive collections of symptoms may be more informative of the probability of respiratory disease than individual and possibly transient phenotypes. However, such collections or components of overall symptomatology need to be valid, and their relationship established with the known risk factors and physiologic measures.

Objectives: To analyze detailed parentally reported respiratory symptoms by principal components analysis and derive symptom components; to examine the relationship of such components with measures of lung physiology and atopy.

Methods: An unselected, population-based birth cohort (n = 946).

Measurements and Main Results: Interviewer-administered questionnaires, lung function (specific airway resistance [sRaw]), airway reactivity (dry air challenge), and atopic status were obtained at ages 3 and 5 years; principal components analysis and multivariate analysis of variance were used to analyze the data. The four-component solution (wheeze, cough, colds, chronic symptoms) explained 53.2% of the variance in symptoms at age 3, and the five-component solution (wheeze, wheeze with irritants, wheeze with allergens, cough, chest congestion) explained 49.8% of variance at age 5. The multivariate analysis revealed novel relationships between symptoms, risk factors for asthma, and measures of lung function. At age 3, sRaw and the interaction between maternal asthma and child's atopy were not only related to wheeze but also independently to the cough component. At age 5, overall wheeze and allergic wheeze were related to lung function and airway reactivity; child's atopy was only related to symptoms when considered as a continuous trait.

Conclusions: Our analysis supports the need to move beyond the presence or absence of individual symptoms. Syndromes of coexisting symptoms more likely reflect underlying pathophysiologic processes.

Clinical trial registered with http://www.controlled-trials.com (ISRCTN72673620).

Key Words: principal components analysis • wheeze phenotypes • childhood asthma • cough

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject In epidemiologic studies of respiratory symptoms, children are often assigned a phenotype based on the response to a single question (e.g., presence/absence of wheeze). What This Study Adds to the Field This study demonstrates the need to move beyond the presence of individual symptoms and demonstrates that, in children aged 3 and 5 years, syndromes of coexisting symptoms are significantly related lung function and risk factors for asthma.

 

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