MPGN is a disease of unknown etiology although antibody to the alternative pathway C3 convertase or C3 Nephritic factor (C3NeF) is thought to play a role in progression of this disorder. In addition, no definitive therapy exists for this disorder. For these reasons, we studied the effect of IVIg in two patients with Type I MPGN. IVIg doses progressed from 150-1400 mg/kg/dose every four weeks for a period of 2 years. Renal function was stable in both patients. Both had nephrotic range proteinuria; post IVIg therapy, the urinary protein/creatinine fell to 0.46 in one patient and 1.49 in the other. Both patients were severely hypocomplementemic; after IVIg, the C3 and C4 normalized in one patient and markedly increased in the other. C3NeF levels fell progressively as therapy continued. C3 levels correlated well with serum C3NeF implying that IVIg may have modulated the functional activity of C3NeF. We conclude that IVIg therapy might be beneficial in the treatment of patients with MPGN. Whether this is mediated by control of C3NeF remains unclear.

(Supported in part by funds from the Children's Miracle Network)