Study of genetic polymorphism of seventh complement component in two families with hereditary deficit

The results of an allelic segregation of C6 and C7 were studied in two Spanish families that have members with C7 deficiency. Absence of C7 in the affected siblings and half of the normal values in their parents were found in both families. The variant responsible for the deficiency (C7Q*0) follows a codominant autosomic inheritance pattern. Establishing allotypes of C6 and C7 by isoelectrofocusing followed by electrophoretic immunoblotting allowed haplotype assignments. In both families the haplotype form responsible for the deficiency seemed to be related to the C6B allotype.