Serum KL-6 in pulmonary alveolar proteinosis: China compared historically with Germany and Japan.

Background: KL-6 is a biomarker of the severity of pulmonary alveolar proteinosis (PAP). We noticed a significant difference in the mean serum KL-6 level between Japanese and Caucasian patients. To assess the clinical value of serum KL-6 in Chinese PAP patients, and to compare the differences in serum KL-6 levels in Chinese patients and patients of other ethnicities. Methods: From 2014-2016, we prospectively examined 37 Chinese Han patients with PAP, measured their serum KL-6 levels, evaluated the correlation between initial KL-6 levels and clinical variables, and compared our results with studies from Japan and Germany (similar methods were used). We searched dbSNP for the MUC1 568 (rs4072037) genotype or allele frequency distributions in China, Japan, and Germany. Results: Initial serum KL-6 levels were significantly correlated with baseline PaO2, A-aDO(2), DLCO, FVC, and LDH levels (all P< 0.001). Compared with Chinese PAP patients, the mean serum KL-6 level was significantly lower in German PAP patients (P< 0.001) but not in Japanese PAP patients (P> 0.4). In the rs4072037 allele frequency distributions, the frequency of the A/A genotype was significantly higher while that of the G/G genotype was significantly lower in Chinese and Japanese cohorts than in Caucasian cohorts (both P< 0.001). Conclusions: Serum KL-6 can be used as a biological indicator for disease monitoring in Chinese patients. The difference in serum KL-6 level among Chinese, German, and Japanese PAP patients may be associated with the distribution of the rs4072037 genotype.