The presence of the MUC5B variant was observed in 50% of patients with RA disease, with the strongest association with rheumatoid arthritis interstitial lung disease (RA-ILD) (especially in patients with usual interstitial pneumonia—UIP and fibrosing hypersensitivity pneumonitis—HP) [176]. The gene discussed is MUC5B; the disease is hypersensitivity pneumonitis.