Hereditary partial deficiency of the third component of complement associated with minimal change nephrotic syndrome

We describe a 10 year old patient admitted to the Children's Hospital of Buffalo with hypocomplementemia associated with steroid responsive minimal change nephrotic syndrome. The sibling also had a low serum C₃ concentration and all family members studied had C₃ slow phenotypes. Factor I levels were at the lower limit of normal in the patient and his brother. Functional assays for CH50, total hemolytic C₃ and serum concentration of C₂, C₄-C₉ and factors B and H were all within normal limits. This case confirms that a depressed serum complement level can occur in minimal change nephrotic syndrome and indicates that this depression could represent a preexisting inherited rather than an acquired deficiency. The findings are consistent with the pressence of a null or hypomorphic C₃ slow allele in hypocomplementemic family members. Additional studies are needed to resolve the association between the inherited partial C₃ deficiency and minimal change nephrotic syndrome.