C2_4_4 microheterogeneity and HLA Class I

:  The microheterogeneity of the tetranucleotide repeat locus C2_4_4 situated in the HLA class I region (6p21.3) was investigated by sequencing 50 alleles in an Austrian population sample of 240 unrelated Caucasoid individuals. Several different sequences were found in alleles of the same length. Analysis of the associations between the sequenced C2_4_4 alleles and HLA class I showed a strong linkage disequilibrium between the C2_4_4*9 sequence variants and two different HLA class I haplotypes, as well as between the most common *17 sequence and one HLA-ABC haplotype. No clear cut association could be observed in C2_4_4*16 and *18. The results of this study demonstrate that the exclusive use of microsatellite polymorphisms for the definition of HLA haplotypes is generally not possible.