While not clinically available, antibodies against endothelin 1 (ET-1) and Ang receptor type 1 (AT1R) have been identified in patients with SSc and other connective tissue diseases at a much higher rate than in IPAH [43], and have been proposed as both predictive and prognostic biomarkers in SSc-PAH. This evidence concerns the gene AGTR1 and pulmonary arterial hypertension.