C4A and hereditary spastic paraplegia: In pediatric HSP patients, the serum IgA (2.61 ± 0.85 vs. 1.2 ± 0.31 g/L) (P < 0.01), IgE (0.83 ± 0.063 vs. 0.079 ± 0.003 g/L) (P < 0.01), and IgG (14.65 ± 1.8 vs. 9.6 ± 1.51 g/L) (P < 0.05) levels were significantly increased compared to the controls, while the C3 (1.45 ± 0.25 vs. 1.73 ± 0.16 g/L) (P < 0.05) and C4 (0.19 ± 0.05 vs. 0.28 ± 0.09 g/L) (P < 0.05) levels significantly decreased (Fig. 2E).