To investigate the prevalence of the MUC5B promoter variant rs35705950 in patients with systemic sclerosis-interstitial lung disease (SSc-ILD) and whether its presence predicts response to immunosuppression with cyclophosphamide (CYC) and mycophenolate (MMF).
SSc-ILD patients who participated in Scleroderma Lung Study (SLS) II (MMF versus CYC) were included in this study (N = 142). TaqMan Genotyping Assays were used to determine the MUC5B rs35705950 single nucleotide polymorphism. Joint models were created to examine how the presence of this variant affected the course of the forced vital capacity (FVC) over 2 years. Linear regression models were used to investigate the relationship between the presence of this variant and the change in quantitative radiographic fibrosis.
Among 128 participants who were tested for this variant, 18% possessed at least one copy of the MUC5B minor allele. Patients with at least one copy of this allele were similar to those without the allele with respect to age, sex, SSc subtype, ILD disease severity; however, this variant was rare among African Americans (3.7%). The presence of the MUC5B variant did not affect the course of the FVC, nor the change in quantitative radiographic fibrosis, ground glass or ILD scores in either treatment arm.
In the context of a randomized controlled trial for SSc-ILD, the presence of the MUC5B variant did not predict disease severity, nor affect treatment response to MMF or CYC. Future studies are needed to determine whether this variant affects ILD progression in other SSc cohorts and in patients receiving anti-fibrotic therapy.