In particular, there was a strong negative correlation between serum KL-6 levels and ΔppFVC in patients with serum CRP levels <0.055 mg/dl (Fig. 4), suggesting that serum KL-6 levels may particularly serve as a prognostic factor for SSc-ILD in the absence of subclinical inflammation. The gene discussed is MUC1; the disease is systemic sclerosis.