Steroid-sensitive nephrotic syndrome associated with positive C1q immunofluorescence.

A 21-year-old woman showed heavy proteinuria and edema. A light microscopic study of a renal biopsy specimen showed diffuse mild mesangial expansion, with borderline mesangial hypercellularity. An immunofluorescence study revealed dominant positive staining (3+) of C1q in the glomerular mesangium. Stainings for C3, C4, IgG, and IgM were weak or 1+. Staining for IgA was negative. Electron-dense deposits were present in the mesangial area. There was significant fusion of foot processes. There was no serological or clinical evidence of collagen disease. She was treated with oral prednisolone (initially, 40 mg/day). The proteinuria was alleviated and the patient remains in complete remission. The histopathological studies were compatible with C1q nephropathy, although the clinical outcome differed in a number of aspects. The clinical picture in the current patient appears to represent a very rare phenotype of nephritis.