Membranoproliferative glomerulonephritis type II is a rare renal disease, associated with uncontrolled activation of the complement alternative pathway because of C3 nephritic factor. Abnormalities in factor H have been rarely described in patients with membranoproliferative glomerulonephritis type II. We report the clinical history, molecular defect, and histologic description of 3 patients with factor H deficiency and various types of membranoproliferative glomerulonephritis. The 3 patients presented with severely decreased C3. Circulating factor H was undetectable. Complete factor H deficiency (CFH) was due to homozygous complement factor H mutations in short consesus repeat (SCR) 7, 10, and 11. Age at onset was 1 (patient 1), 17 (patient 2), and 33 years (patient 3). Symptoms at diagnosis included proteinuria of 0.5, 2.4, and 11 g/d, respectively, microhematuria, and normal renal function in all cases. The estimated glomerular filtration rate at last follow-up was 25, 43, and 112 mL/min per 1.73 m(2), at ages of 29, 24, and 37 years, respectively. Renal biopsies disclosed a membranoproliferative glomerulonephritis type II with atypical discontinuous dense deposits in patient 1; a membranoproliferative glomerulonephritis type I with immunoglobin G (IgG), C1q, and abundant C3 deposits in patient 2; and a membranoproliferative glomerulonephritis with isolated C3 deposits without dense deposits in patient 3. This report of factor H-deficient patients emphasizes the diversity of the histologic lesions associated with factor H deficiencies and the role of the alternative pathway in several subtypes of membranoproliferative glomerulonephritis.

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