The strong C3 staining with IgA co-dominance and low serum C3 level at presentation suggest dysregulated activation of the complement system as is seen with C3 glomerulopathy (C3G) or IC-MPGN (15), and can act as a disease-modifying factor in IgA nephropathy or IgA vasculitis. The gene discussed is CD79A; the disease is IgA glomerulonephritis.