Respiratory function in healthy first-degree relatives of asthmatic adolescents

Asthma is a complex disease associated with biological and physiological phenotypes. The objective of this study was to compare the respiratory function in healthy first-degree relatives of asthmatic and non-asthmatic adolescents. We used a cross-sectional approach to assess 101 family cases (presence of one or more adolescents classified as asthmatic) and 275 stable families (families without adolescents classified as asthmatic). We obtained a final sample of 822 relatives. The respiratory function was evaluated by the forced expiratory volume in 1 second (FEV), and the forced vital capacity (FVC), using the Microlab 3300® Spirometer. A self-administered questionnaire was used to record upper and lower airway symptoms, allergic symptoms and medical history. To compare continuous variables, the Mann-Whitney and Kruskal-Wallis tests were applied when variables did not follow a Gaussian distribution and the variances were not homogeneous. A linear regression adjusted for age, gender and height was also applied to compare the lung function between asthmatic and non-asthmatic relatives. Parents of asthmatic adolescents had significantly lower values of the lung function than both parents together and mothers of non-asthmatics (84.6 vs. 97.6, p <0.01, for FEV and 84.3 vs. 97.9, p <0.01, for FVC, and 97.3 vs. 109.7, p <0.01, for FEV and 89.5 vs. 105.5, p <0.01, for FVC, respectively). Also, siblings of asthmatic adolescents had lower FEV (98.6 vs. 109.4, p <0.01) and FVC values (85.9 vs. 102.7, p <0.01). The healthy first-degree relatives of asthmatic adolescents have worse respiratory function than those of non-asthmatic adolescents. Asymptomatic relatives of asthmatics can have physiological characteristics that may reveal the phenotypic pattern of the disease.