Introduction and Objectives It is increasingly recognised that small airway dysfunction is associated with suboptimal asthma control. We have previously reported that β2-adrenoreceptor polymorphism at position 16 (i.e. Arg/Gly) is not related to FEV1 or airway hyper-responsiveness in persistent asthmatics.1 However effects of β2-adrenoreceptor polymorphism on the small airways are not known. This pilot study in a different cohort of patients evaluated the effects of β2-adrenoreceptor polymorphism on small airway function and asthma control. Impulse oscillometry (IOS) was used to assess small airway function along with FEF25–75. IOS is an effort independent test performed during normal quiet tidal breathing and is able to discriminate between changes in central and peripheral airways. Resistance at 5 Hz (R5) and 20 Hz (R20) indicate total and central airway resistance respectively - the difference between R5 and R20 indicates peripheral airway resistance. Asthma control was assessed using the Asthma Control Questionnaire (ACQ-5).
Methods We collected spirometry, IOS and ACQ data from patients attending a secondary care asthma clinic. A total of 100 patients all taking inhaled corticosteroids (20% taking long acting beta-agonists) were included with a mean: age 39.2 year FEV1 88.4%, FEF25–75% 55.5%, R5%162%, R5-R20 0.07 kPa/l/s, ACQ-5 1.70
Results 48% (n = 48) had 1 or 2 copies of the Arg allele (i.e. Arg/Arg or Arg/Gly genotypes) while 52% (n = 52) had no copies of the Arg allele (i.e. Gly/Gly genotype). There was no significant difference between genotypes in terms of FEV1, FEF25–75, R5, R5-R20 or ACQ. Furthermore there was no significant effect of LABA according to Arg/Gly polymorphism.
Reference 1. Manoharan A, Anderson WJ, Lipworth BJ. Influence of β2-adrenergic receptor polymorphism on methacholine hyperresponsiveness in asthmatic patients. Ann Allergy Asthma Immunol 2013;110: 161–164