Isolated C3 deposition in patients without systemic disease.

Deposition of C3 without immunoglobulins ("isolated C3") was found in 9.8% of 540 renal biopsies performed between 1976 and 1982. Thirty-two of these samples were from patients with systemic diseases (16), well defined forms of glomerulonephritis (9), other renal diseases (4) or renal allografts (4). The remaining 22 patients are described. Five had nephrotic syndrome, three of them with minimal changes on light microscopy and good response to corticosteroids. We were left with a group of 17 patients who presented with gross (4) or microscopic (12) hematuria or asymptomatic proteinuria (1) whose biopsies showed mesangial proliferation or/and hyperplasia and who followed a benign course over the mean 3 years of follow-up, with the exception of one whose renal function is declining. This clinicopathological picture is similar to that described in two previous publications suggesting that "Isolated C3 mesangial proliferative nephritis" is a recognizable sub-group within the spectrum of glomerulonephritis.