The effect of ethnicity on major histocompatibility complex complement allotypes and extended haplotypes in patients with systemic lupus erythematosus

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Abstract
Previous studies of patients with systemic lupus erythematosus (SLE) have shown an increased frequency of certain major histocompatibility complex (MHC) markers, including HLA–DR2, DR3, and C4AQO (C4A-null), in Caucasian patients. However, most of these studies were of randomly selected, unrelated patients; families were not included, and haplotypes were not determined. In order to define more accurately the possible role of MHC genes in lupus susceptibility, HLA–A, B, C, and DR, as well as BF, C2, C4A, C4B, and GLO, markers were determined in 62 Caucasian patients of known ethnic background, and in the members of their families. The distributions of extended haplotypes (fixed combinations of HLA–B, DR, and complotype alleles), fragments thereof, and individual alleles were determined in SLE patients and controls. The MHC distributions in all patients were compared with haplotypes in a normal Caucasian population. There were no statistically significant differences between the frequencies of any MHC marker, fragment, or extended haplotype in the patients compared with the controls. The patients were categorized into 2 groups of European ancestry (English/Irish; other Europeans), and each group was compared with a group of ethnically matched controls. There was a statistically significantly increased frequency of the alleles C4AQO and DR3 and the complotype SC01 in SLE patients of English/Irish descent as compared with ethnically matched controls. The increase in C4AQ0 and DR3 could be accounted for by the fact that they were part of the extended haplotype [HLA–B8;SC01;DR3] and/or its fragment (SC01;DR3). No increase in any MHC marker was observed in the other patients. Thus, our results suggest that SLE in patients of English/Irish ancestry is associated with an MHC extended haplotype and/or its DR-containing fragment.