C1q nephropathy: do C1q deposits have any prognostic significance in the nephrotic syndrome?

C1q deposits are usually found in association with other complement components and immunoglobulins in proliferative glomerulonephritis and may predominate in systemic lupus erythematosus (SLE). We report the clinical outcome of four patients who developed a nephrotic syndrome associated with C1q nephropathy unrelated to SLE. On presentation the mean urinary protein loss was 6.8 g/24 h (range 4-10), and renal function impaired, mean serum creatinine 201 mumol/l (150-400). Over a mean follow up period of 6.5 years (1.7-19), all four patients improved, three spontaneously and one treated with steroids and cyclosporin, to a current urinary protein loss of 0.3 g/24 h (less than 0.2-0.9) and serum creatinine 98 mumol/l (68-115). C1q nephropathy was confirmed in each biopsy by conventional immunohistology. C1q deposits were demonstrated within the glomerular basement membrane of three biopsies and the mesangium in two samples. One patient had been categorized on light- and electron-microscopy as having mesangiocapillary glomerulonephritis, one membranous glomerulonephritis, one proliferative glomerulonephritis with focal segmental glomerulosclerosis, and one diffuse proliferative glomerulonephritis with both subendothelial and mesangial dense deposits. In view of the expected progressive nature of the underlying renal histopathological appearance, the presence of predominant C1q deposits would appear to be associated with a better clinical outcome.