Ten out of 34 (29%) SSc plasma and 48 out of 88 (54%) SSc sera had detectable IFN-α (Supplementary Fig. 2a, b), which was in statistically significant correlation with CXCL4 in both SSc cohorts (r = 0.45, P = 0.0042, N = 34 and r = 0.45, P = 0.0001, N = 88) (Fig. 1d, e). This evidence concerns the gene IFNA1 and systemic sclerosis.