Complement deficiency and nephritis. A report of a family.

A family is described in which three children had homozygous deficiency of C3 and in which both parents and two other children were heterozygous for the C3 null gene. One child with heterozygous C3 deficiency was found to have membranoproliferative glomerulonephritis; proteinuria and/or microscopical haematuria was present in all three homozygous C3-deficient children. All children with homozygous or heterozygous C3 deficiency were, to a varying degree, susceptible to infection. The only child of the family with normal complement had no increased risk of infection and no renal disease. This family study provides further support for the proposal that C3 deficiency predisposes to nephritis.