U1 and systemic lupus erythematosus: Other factors, including the presence of anti-ET-1 [47], anti-U1 RNP [14], anti-topoisomerase I (anti-Scl-70) [48], anti-SmD1 [49], and anti-Smith (Sm) [50], low erythrocyte sedimentation rate (ESR) [18] and hypocomplementemia [50] have also been associated with the presence of PH in SLE.