Polymorphism of the seventh component of complement (C7) in a healthy Caucasian population: an immunoblotting study with neuraminidase-treated samples.

Genetic polymorphism of the seventh component of complement (C7) was studied in a healthy Caucasian population using polyacrylamide gel isoelectric focusing of neuraminidase-treated plasma samples and an immunoblotting procedure for the specific detection of C7. Among 248 blood donors, three C7-3/1 heterozygotes were identified, resulting in a C73 allele frequency of 0.0061 +/- 0.0035. Neuraminidase treatment of serum or plasma samples is necessary for unequivocal identification of C73, which is known to be a hypomorphic variant. This observation is discussed with special reference to previous studies on C7 polymorphism in Caucasian populations, where untreated samples have been used for C7 typing.