C1Q nephropathy in children.

C1q nephropathy (C1qNP) is a peculiar form of glomerulonephritis characterized by mesangial immunoglobulin and complement deposits, predominantly C1q, with no evidence of systemic lupus erythematosus. We describe the incidence, manifestation, histopathologic findings, follow-up, treatment and outcome of C1qNP. Twelve C1qNP patients were identified among 131 children who had undergone renal biopsy, accounting for a 9.16% incidence of C1qNP. Light microscopy examination showed focal segmental glomerulosclerosis (FSGS) with or without diffuse mesangial proliferation (n=6), minimal change disease (MCD) (n=4) or focal glomerulonephritis (n=2). C1q deposits were found in all, while electron microscopy revealed visible deposits in nine cases. Eight children presented with nephrotic syndrome, while one had nephrotic proteinuria and renal insufficiency that progressed to end-stage renal failure. The remaining three patients presented with nonnephrotic proteinuria associated with microhematuria, hypertension or renal insufficiency. Only one nephrotic syndrome patient responded excellently to corticosteroids, while four became corticosteroid dependent, and three were corticosteroid resistant, showing a very poor response to other immunosuppressive therapy as well. Patients with non-nephrotic proteinuria demonstrated fixed laboratory findings. Most C1qNP patients had FSGS or MCD, the majority of them presenting with corticosteroid-dependent or corticosteroid-resistant nephrotic syndrome. The latter showed a very poor response to any immunosuppressive therapy and high risk for progressive renal insufficiency.