Study subjects
For GWAS, the subjects were obtained from three hospitals; Asan Medical center (AMC), Seoul National University Gangnam Center of Seoul National University Hospital (SNUH) and Kang-Won National University Hospital (KNUH). Of 1,386 asthma patients, 1,293 patients were from AMC between January 2005 and December 2018. The inclusion criteria were (1) aged >18 years, (2) symptoms such as dyspnea, wheezing, or cough for more than 3 months, and (3) airway hyperresponsiveness as indicated by a 20% reduction in forced expiratory volume in 1 second (FEV1) with a methacholine dose of 16 mg/mL (PC 20) through a provocation test or airway reversibility as indicated by an increase in FEV1 of > 12% (and at least 200 mL) following the inhalation of a short- acting β-agonist. Patients with severe lung damage, bronchiectasis, or a history of lung resection were excluded. From the SNUH, 93 asthmatic patients were included, who provided a “yes” response to any of the following questions: “Have you ever been diagnosed with asthma?” or “Have you ever taken asthma medication at least once?”. Of 5,205 controls, 5,161 and 44 controls were from SNUH and KNUH, respectively, and they were not diagnosed with asthma and chronic obstructive pulmonary disease (COPD). The study was approved by the Institutional Review Board (2019-1676) of all participating institutions.