OBJECTIVE: Pulmonary arterial hypertension (PAH) is a severe complication of connective tissue diseases (CTDs). This study aimed to investigate the clinical and hemodynamic characteristics and survival of anti-U1 RNP-positive patients with CTD-associated PAH, with a focus on systemic sclerosis (SSc)-associated PAH. METHODS: We implemented a prospective database that included patients with CTD-associated PAH for whom there were clinical, autoantibody, and mortality data. We compared clinical and hemodynamic characteristics to anti-U1 RNP antibody status. We then assessed whether anti-U1 RNP antibodies could be a prognostic factor in CTD-associated PAH with a focus on SSc-associated PAH. RESULTS: We studied a total of 342 patients with CTD-associated PAH, of whom 36 (11%) were anti-U1 RNP antibody positive. Anti-U1 RNP-positive patients were younger and less functionally impaired than were anti-U1 RNP-negative patients in CTD- and SSc-associated PAH. Hemodynamic parameters were similar in anti-U1 RNP-positive and anti-U1 RNP-negative patients. In CTD-associated PAH, anti-U1 RNP positivity was associated with decreased mortality in univariable analysis (hazard ratio 0.34 [95% confidence interval 0.18-0.65], P < 0.001). In multivariable analysis, anti-U1 RNP positivity was also associated with decreased mortality (hazard ratio 0.44 [95% confidence interval 0.20-0.97], P = 0.043) independently of age, sex, functional parameters, lung involvement, and hemodynamic parameters. Results were similar in SSc-associated PAH, although the association between anti-U1 RNP positivity and survival did not reach significance in univariable (hazard ratio 0.47 [95% confidence interval 0.22-1.02], P = 0.055) and multivariable (hazard ratio 0.47 [95% confidence interval 0.20-1.11], P = 0.085) analyses. CONCLUSION: Anti-U1 RNP positivity was associated with distinct clinical characteristics and survival in CTD- and SSc-associated PAH. While hemodynamic parameters were similar in anti-U1 RNP-positive and anti-U1 RNP-negative patients, our results suggest that anti-U1 RNP positivity could be a factor protecting against mortality in CTD- and SSc-associated PAH
