Recently, we reported that a MUC5B variant rs35705950, the strongest susceptibility variant to idiopathic pulmonary fibrosis (IPF), was strikingly increased in AAV-ILD patients but not in AAV patients without ILD; however, due to the low allele frequency in the Japanese population, the MUC5B variant alone cannot account for the high prevalence of AAV-ILD in Japan. The gene discussed is MUC5B; the disease is idiopathic interstitial pneumonia.