ALAS2 and systemic sclerosis: ALAS2 gene expression was taken as a primary biomarker representing the entire EDS (note the Pearson correlation r between ALAS2 and ERAF/AHSP gene expression, among the subjects used for this analysis, was 0.987, and 0.957 for IPAH and SSc-PAH, respectively), and was hence used for the purpose of computing correlations of the EDS with hemodynamic measurements (Figure 8).