No statistically significant differences were found in C3 [1.19 g/L (IQR 1.11–1.27 g/L) vs. 1.12 g/L (IQR 1.01–1.23 g/L); p > 0.05], C4 [0.2 g/L (IQR 0.16–0.26 g/L) vs. 0.2 g/L (IQR 0.16–0.23 g/L); p > 0.05], C2 [25 mg/L (IQR 22.6–25.7 mg/L) vs. 27.2 mg/L (24.2–32.5 mg/L); p > 0.05] and CH50 [83.86 U/mL (IQR 74.6–103.18 U/mL) vs. 74.05 U/mL (IQR 65.31–86.86 U/mL); p > 0.05] between SSc patients with or without joint/tendon involvement. This evidence concerns the gene C4A and systemic sclerosis.