C4 phenotypic variation suggests an unusual class III gene organization.
The class III gene markers, C4A, C4B, C2 and BF were determined in 26 HLA genotyped families. In 6 of these families the inheritance of the C4A electrophoretic phenotype, C4A 3, A 2 could not be explained assuming the genetic model that the C4A component is controlled by only one locus (C4A) and suggests that both C4A 3 and C4A 2 are encoded by the same chromosome. This apparently duplicated C4A locus haplotype is common in Northern Europeans occurring at a frequency of at least 6%. In 4 families the C4A 3, A 2 'variant' occurred together with HLA-Bw35 and in 2 together with HLA-Bw55. Furthermore, it was striking that in each family the C4A 3, A 2 'variant' was found exclusively with the complotype FC3/20 which encodes no phenotypically expressed C4B locus product.
D000483:Alleles; D002874:Chromosome Mapping; D003181:Complement C4 / Q000235:genetics*; D015934:Complement C4a; D015935:Complement C4b; D011415:Complement Factor B / Q000235:genetics; D005260:Female; D005796:Genes; D014644:Genetic Variation; D005838:Genotype; D006238:Haploidy; D006801:Humans; D008297:Male; D010375:Pedigree; D010641:Phenotype
D003181:Complement C4; D015934:Complement C4a; D015935:Complement C4b; D011415:Complement Factor B