SFTPC and autoimmune interstitial lung disease-arthritis syndrome: Autoantibody tests including antinuclear antibodies (ANA), double-stranded deoxyribonucleic acid (ds-DNA), extractable nuclear antigen (ENA), anti-neutrophil cytoplasmic antibodies (ANCA), rheumatoid factors (RF) and anti-cyclic citrullinated peptide (CCP) antibody were performed in 96%, 96%, 93%, 92%, 79% and 68% of the patients and were found to be positive not only in all the patients with CTD, vasculitis, and IPAF, and also in some patients with PID associated ILD such as COPA syndrome, SAVI, and CGD coexisting with IPAF and some patients with SFTPC genetic mutation coexisting with IPAF.