HLA-DR and -DQ genotypes of celiac disease patients serologically typed to be non-DR3 or non-DR5/7

The susceptibility to develop celiac disease (CD) seems to be primarily associated to a particular HLA-DQ α/s heterodimer encoded by the DQA1∗0501 and DOB1∗0201 alleles, in cis position on the DR3-DQ2 haplotype or in trans position by DR5-DQ7/DR7-DQ2 heterozygotes. However, exceptional patients exist who are neither DR3 nor DR5/DR7, particularly among Southern European populations. We therefore examined the DRB1, DQA1, and DQB1 alleles of 13 Spanish CD patients who were serologically typed to be neither DR3 nor DR5/DR7. Five patients were found to carry the DQA1∗0501 and DQB1∗0201 alleles either in cis or in trans position, three of them had previously been serologically mistyped. However, two of these patients carried DQA1∗0501 and DQB1∗0201 on haplotypes other than DR3 or DR5 in combination with DR7. One of the latter patients carried an unusual DR4-DQ2 haplotype, while another had an unusual DR8-DQ2 haplotype. Four of the remaining eight patients carried DR4-DQ8 haplotypes. Taken together, our findings provide further evidence that the DQ α/s heterodimer encoded by the DQA1∗0501 and the DQB1∗0201 alleles confers the primary HLA-associated susceptibility to develop CD. However, our studies also corroborate that a second (and “weaker”) HLA-associated CD susceptibility gene may be present on some DR4-carrying haplotypes.