We did not find any differences between male and female SSc patients in CH50 [79.82 U/mL (IQR 63.79–82.26 U/mL) vs. 75.9 U/mL (IQR 66–90.57 U/mL); p > 0.05], C2 [24.4 mg/L (IQR 23.1–27.3 mg/L) vs. 26.3 mg/L (IQR 24.2–32.7 mg/L); p > 0.05], C3 [1.18 g/L (IQR 1.07–1.27 g/L) vs. 1.13 g/L (IQR 1–1.23 g/L); p > 0.05], C4 [0.22 g/L (IQR 0.2–0.23 g/L) vs. 0.2 g/L (IQR 0.16–0.23 g/L); p > 0.05], ESR [16 mm/h (IQR 8–26 mm/h) vs. 22 mm/h (IQR 12–31 mm/h); p > 0.05] and CRP [2000 mcg/L (IQR 900–3700 mcg/L) vs. 1800 mcg/L (IQR 1000–4600 mcg/L); p > 0.05]. The gene discussed is C4A; the disease is systemic sclerosis.