A hypomorphic electrophoretic variant of C3 with the mobility of C3 F was found in the serum of a healthy man, his mother, and one of his two sons. Serum C3 concentrations were normal in these subjects as were hemolytic complement levels. Metabolic studies with radiolabeled purified C3 FF and C3 SS in the propositus suggested, but did not prove, that the variant C3 F gene was hyposynthetic. The designation C3 f was therefore proposed for this allele.
