Genetic polymorphism of human factor I (C3b inactivator).

Genetic polymorphism of human factor I (C3b inactivator) has been described using polyacrylamide gel isoelectric focusing electrophoresis of neuraminidase-treated EDTA plasma samples followed by electrophoretic blotting technique. In 435 individuals three different common patterns were observed, and these were controlled by two common alleles at a single locus. The results of typing family material confirmed autosomal codominant Mendelian inheritance. Two common alleles were designated FI*B and FI*A, and gene frequencies were estimated to be 0.8931 and 0.1069 for FI*B and FI*A, respectively. The distribution of phenotypes fitted the Hardy-Weinberg equilibrium. Linkage studies failed to show close linkage between factor I and the major histocompatibility complex.