We hypothesized that the BHR of adolescents in asthma remission may be related to the intrinsic BHR of each individual, and thus may be controlled by genetic factors. Specifically, we wanted to test the hypothesis that the persistence of BHR in clinical remission during adolescence is dependent on the family history of BHR. In order to test this hypothesis, we performed a methacholine challenge test in the parents of adolescents in asthma remission, and analyzed the results with regard to the BHR status of their children.

Materials and Methods

Adolescents in long-term atopic asthma remission and their parents were targeted for this study. The adolescents, 13 to 17 years of age, were selected from the Seoul National University Children’s Hospital allergy clinic. All subjects had a history of wheezing and dyspnea, and had previously received a diagnosis of atopic asthma according to the American Thoracic Society crite-ria. In the past, all were recorded to have a provocative concentration of methacholine causing a 20% fall in FEV₁ (PC₂₀) of < 18 mg/mL. Other chronic obstructive airway disorders had been excluded by relevant investigations in all subjects. Atopy was defined as at least one positive skin-prick test response in a panel of 12 common aeroallergens, in the presence of positive and negative controls. The majority of subjects showed a positive skin reaction to house dust mites. Long-term clinical remission was assumed if subjects reported the complete absence of wheezing and dyspnea at rest or on exertion and had not received any medication in order to control asthmatic symptoms for at least 24 months before the study. Subjects underwent spirometry and methacholine inhalation testing. To be eligible for the study, subjects had to be capable of performing pulmonary function tests in a reproducible way (ie, a coefficient of variation of FEV₁ in three consecutive flow-volume curves of < 5%) and needed to have an FEV₁ > 70% of the predicted value.²⁰ Clinical data were obtained retrospectively by reviewing the files of the outpatient clinic.

Both natural parents of the adolescents were asked if they would participate in the study. After obtaining consent, the parents underwent spirometry and methacholine inhalation testing. Testing was performed by a single investigator who had no knowledge of the test results of the children. Parents with a diagnosis of asthma were included in the study. Excluded were the parents with an FEV₁ < 70% of the predicted value.

FEV₁ was recorded as the best of three attempts using a computerized spirometer (Microspiro HI 298; Chest; Tokyo, Japan), with measurements not varying by > 5% being acceptable.