A high frequency of the A30, B18, DR3, DRw52, DQw2 extended haplotype in Sardinian celiac disease patients: Further evidence that disease susceptibility is conferred by DQ A1*0501, B1*0201

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Abstract
This study characterizes by serological and molecular methods the HLA class I and class II alleles in a group of celiac disease children, their parents and a control group of Sardinian descent. We found the DR3‐DQw2 haplotype in all patients which was, in almost all cases (84%), associated with the HLA‐A30, B18, DR3, DRw52, DQw2 extended haplotype named “Sardinian haplotype” because of its frequency (12–15%) in this Caucasian population. This is the first time that this DQw2‐linked haplotype has been reported with such a high frequency in CD. However, no different distribution of “Sardinian haplotype” was found comparing CD patients with 91 haplotyped DQw2‐positive controls. This finding indicates that the DQw2 antigen in Sardinians is almost always associated with the A30, B18, DR3, DRw52, DQw2 extended haplotype. The DQA1 and DQB1 second exon sequence analysis of the B18,DR3 and B8,DR3 haplotypes showed the DQA1*0501 and DQB1*0201 alleles which shared the already published sequences. DPB1 subtyping showed the DPB1*0301 allele more frequently (p < 0.005) in CD patients but this difference was no longer significant when patients and controls, both heterozygous for the DR3‐DQw2 haplotype, were compared. We suggest that the divergent HLA extended haplotypes and DP allele associated with CD, described in different Caucasian populations, can be explained by the particular DQw2 linkage disequilibrium in each population.