A single nucleotide polymorphism (SNP) rs35705950 in the promoter of Mucin 5B (MUC5B) has been reported to be associated with idiopathic pulmonary fibrosis (IPF) mainly in Caucasian populations. This study was conducted to confirm the association between rs35705950 and IPF in a Japanese population.

Genomic DNA was extracted from blood samples in 384 Japanese and 137 German subjects, and rs35705950 was detected by commercially available genotyping assay.

The genotype distributions of rs35705950 in Japanese patients with IPF, nonspecific interstitial pneumonia (NSIP) and healthy subjects (HS) were significantly different from those in the German counterparts (P < 0.001, P < 0.001 and P = 0.010, respectively). The rs35705950 T allele frequencies in patients with IPF, NSIP and HS were 3.4%, 1.7% and 0.8%, respectively in the Japanese, while they were 33.1%, 27.4% and 4.3%, respectively in the German cohort. The T allele frequencies in patients with IPF were significantly higher than those in HS both in the Japanese (P = 0.031) and German (P < 0.001) cohorts.

The association between rs35705950 and IPF was also present in this Japanese cohort, but was not as strong as the German counterpart. To our knowledge, this is the first study to successfully validate the association between rs35705950 and IPF in a Japanese ethnicity.