The MUC5B rs35705950 allele is a cooperator in familial pulmonary fibrosis.

<bold>Background:</bold> Familial pulmonary fibrosis (FPF) is defined by two or more family members with interstitial lung disease of any etiology. Rare variants in genes related to surfactant production, TERT, TERC and short age-adjusted leukocyte telomere length and the polymorphism rs35705950 at MUC5B are the most common genetic alterations related to FPF. <bold>Objective:</bold> Evaluate gene cooperation in FPF. <bold>Methods:</bold> Retrospective series of 82 FPF index cases. Data were collected from medical records and blood samples for genetic analysis. Telomere length was determined using peripheral blood leukocyte DNA by Southern blotting. Real-time PCR genotyping was performed using TaqMan probes for each single-nucleotide polymorphism. The next-generation sequencing data were analyzed using the GATK tools and the variants found were classified according to the American College of Medical Genetics and Genomics criteria. <bold>Results:</bold> The cohort was divided into two groups: the telomere-related (TR)-FPF, composed of the 18 patients who had both short telomeres and a rare variant; and the non-TR-FPF, comprised of the remaining 64 patients who did not meet the previous criteria. The Sankey diagram represents the proportion of TR-FPF and non-TR-FPF patients with each of the genetic features, demonstrating the importance of the MUC5B rs35705950 allele. <bold>Conclusion:</bold> The MUC5B rs35705950 allele represents an important cooperator for FPF, independent of the telomere commitment.