The genetic polymorphism of the fourth component of human complement: methodological aspects and a presentation of linkage and association data relevant to its localization in the HLA region.

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Abstract
The C4 [4th component of complement] polymorphism in man was studied by immunofixation electrophoresis, crossed immunoelectrophoresis and functional detection after agarose gel electrophoresis. It has so far not been possible to reveal this polymorphism by isoelectric focusing and functional detection of C4 bands. Common alleles (3) and one less frequently occurring allele were identified. In a small population sample studied by all the different techniques and verified by family segregation, the following gene frequencies were found: C4F: 0.46, C4S: 0.32, C4F1: 0.20 and C4M; 0.02. By linkage and association studies in a family material it was shown that a structural C4 locus is situated in the HLA region of chromosome 6 very close to the HLA-B and Bf loci.