U1 and systemic sclerosis: The result showed that anti-U1 RNP positivity was associated with better survival of SSc-PAH with a pooled HR of 0.47 (95%CI 0.26–0.85, p = 0.013), while its association with survival of SLE-PAH was not significant with a pooled HR of 1.69 (95%CI 0.77–3.70, p = 0.189).