Interpretation

Most (90%-95%) patients with celiac disease have 1 or 2 copies of HLA-DQ2 haplotype (see below), while the remainder have HLA-DQ8 haplotype. Rare exceptions to these associations have been occasionally seen. In one study of celiac disease, only 0.7% of patients with celiac disease lacked the HLA alleles mentioned above. Results are reported as permissive, nonpermissive, or equivocal gene pairs.

It is important to realize that these genes are also present in about 20% of people without celiac disease. Therefore, the mere presence of these genes does not prove the presence of celiac disease or that genetic susceptibility to celiac disease is present.

The HLA-DQ molecule is composed of 2 chains: DQ alpha (encoded by HLA-DQA1 gene) and DQ beta (encoded by HLA-DQB1 gene). HLA-DQ typing can be performed by serological or molecular methods. Currently, most laboratories perform typing by molecular methods. HLA-DQ2 and DQ8, as typed by serology, are usually based on the molecular typing of the DQB1 chain only. The current molecular method allows typing for both the DQB1 and DQA1 chains. This has shown that there are different haplotypes of HLA-DQ2 and DQ8. Typing of these haplotypes is important in celiac disease as they carry different risk association.

There are 2 common haplotypes of DQ2:

1. DQA1*05:01 with DQB1*02:01, also called DQ2.5 in celiac literature

2. DQA1*02:01 with DQB1*02:02, also called DQ2.2 in celiac literature

A single haplotype (heterozygote) of DQ2.5 is permissive for presence of celiac genes. However, only a double haplotype (homozygous) of DQ2.2 is permissive for presence of celiac genes. There are few reports where a single haplotype of DQ2.2 is considered to be an equivocal risk. In some cases, the DQ2.2 haplotype may be present with a DQ7.5 haplotype (DQA1*05:05 with DQB1*03:01). In this case, a DQ2.5 molecule can be formed by the combination of DQB1*02:02 from one chromosome and DQA1*05:05 from the other chromosome. These cases fall in the same category as the DQ2.5 heterozygote.

There are 3 common haplotypes of DQ8:

1. DQA1*03:01 with DQB1*03:02

2. DQA1*03:02 with DQB1*03:02

3. DQA1*03:03 with DQB1*03:02

Any single haplotype (heterozygote) of DQ8 is permissive for celiac.

Therefore, the gene pairs permissive for celiac are:

1. Heterozygote (single copy)

-DQA1*05:XX with DQB1*02:01

-DQA1*05:XX with DQB1*02:02

-DQA1*03:XX with DQB1*03:02

2. Homozygous (2 copies)

-DQA1*02:01 with DQB1*02:02

Gene pairs equivocal for celiac are:

1. Heterozygote (single copy)

-DQA1*02:01 with DQB1*02:02

2. Rare allele's types of DQ2 and DQ8 other than those listed above

All other gene pair combinations are considered nonpermissive for celiac.

There are reports that specific HLA-DQ2 and DQ8 combinations may confer different risks for the development of celiac disease.(1)

A recent publication from our group demonstrated that risk gradient of tissue transglutaminase (tTG) IgA positivity depends on specific HLA-DQ2 and DQ8 combinations.(2) For more information see Tissue Transglutaminase IgA positivity.