Association between restriction fragment length variants of the complement C4 genes and MHC haplotypes.

DNA polymorphism of the human major histocompatibility complex (MHC)-linked complement C4 genes was studied using restriction enzymes XbaI and TaqI, and Southern hybridization. The results show that some, but not all, C4 phenotypes can be divided into subtypes. Analysis of MHC haplotypes indicates that in each extended MHC haplotype, i.e. in the haplotypes having a particular combination of HLA and complotype phenotypes in significant linkage disequilibrium, the C4 genes always produce just one 'conserved' restriction enzyme fragment pattern, while in the other haplotypes the C4 genes are more heterogeneous. Furthermore, the findings provide preliminary evidence for a C4B gene duplication, and suggest that the C4 genes may often be 'corrected' alike.