Serum KL-6 levels were significantly higher in PAP patients with A/A genotype than in those with A/G genotype (8084 ± 1673 vs. 2397 ± 462 U/mL, p = 0.007), whereas such genotype-related differences in KL-6 levels were not seen in healthy controls (A/A: 251 ± 25, A/G: 267 ± 20, G/G: 337 ± 40 U/mL, p > 0.05 for all comparisons) (Fig. 3a). This evidence concerns the gene MUC1 and pulmonary alveolar proteinosis.