C3 and hereditary spastic paraplegia: Given that there are significant immune disorders including elevated IgA and IgE levels in patients with HSP, we conducted Spearman correlation analysis to determine the potential correlation between the gut microbiota and HSP-related indexes including IgA, IgE, IgG, IgM, C3, D-dimer, and IgA/C3 (Figure 7A).