2.1. DNA and clinical information about patients

DNA samples were available from 105 of 108 unrelated Japanese patients previously reported by Hijikata et al. (Hijikata et al., 2011). All fulfilled the following diagnostic criteria for DPB proposed in 1995 by a working group of the Ministry of Health and Welfare of Japan: persistent cough, sputum, and exertional dyspnea; history of, or current chronic sinusitis; bilateral diffuse small nodular shadows on a plain chest X‐ray film or centrilobular micronodules on chest computed tomography (CT) images; coarse crackles; FEV_1.0/FVC less than 70% and PaO₂ less than 80 Torr; and titer of cold hemagglutinin equal to or higher than 64 ×. Definite cases should fulfill the first three criteria and at least two other remaining criteria, excluding other chronic respiratory diseases (Keicho & Kudoh, 2002). Our screening was extended to 37 patients with recurrent infections of the upper and lower airways, recruited in the same period (mainly from 1997 to 1999), but not meeting the DPB criteria. The DNA panel of the healthy anonymous Japanese population, consisting of 499 samples was obtained from the Health Science Research Resources Bank (Japan Health Sciences Foundation).