GPX3 and systemic sclerosis: In comparison to established reference ranges from literature [21,43], the SSc patients displayed a relative Se deficit (Table S1); the prevalence of Se deficiency (SSc-PAH vs. SSc vs. controls) was 16.0% vs. 14.6% vs. 0% as judged by serum Se, 64.0% vs. 41.5% vs. 10% as judged by serum SELENOP, and 28.0% vs. 19.5% vs. 0% as judged by GPX3 activity, respectively.