Genetic studies of low-abundance human plasma proteins. VII. Heterogeneity of the C1S subcomponent of the first complement component.

Charge-based structural variation has been observed in the C1s subcomponent of the first complement component C1 after isoelectric focusing and immunoblotting. One common and two uncommon autosomal co-dominantly expressed alleles, designated C1S*1, C1S*2 and C1S*3, have been recognized at the C1S structural locus. The frequency of these alleles was 0.979, 0.016 and 0.005, respectively, in a U.S. white population. No variation at the C1S locus was observed in a U.S. black sample (n = 95).