Introduction
The HLA-DQ2.5, -DQ2.2 or -DQ8 haplotypes are necessary for coeliac disease development with homozygotes of DQ2.5 carrying the highest disease risk. However, with only 1:4-1:7 of true patients usually diagnosed, the true haplotype distribution is unknown. It can be hypothesized that the distribution differs in the large group of undiagnosed individuals who likely present with less distinct symptoms and older age.
Aims & Methods
The aim of this study was therefore to investigate the HLA-DQ haplotype distribution including both known and new, previously undiagnosed patients. A population-based study of 52,588 adults was screened for coeliac disease by serology, identifying 470 new cases (Marsh 3) in addition to 376 known cases identified via registries. All cases and a random sample of 1412 controls underwent HLA-DQA1- and HLA-DQB1-sequencing to infer relevant HLA-DQ haplotype combinations (DQ2.5/DQ2.5, DQ2.5/DQ2.2, DQ2.2/DQ7.5 [DQ2.5trans], DQ8/DQ8, DQ2.5/DQ8, DQ2.5/DQ7.5, DQ2.5/DQX, DQ2.2/DQ2.2, DQ2.2/DQ8, DQ2.2/DQX, DQ8/DQX, DQX/DQX [neither DQ2 nor DQ8]). Odds ratios (OR) with 95% confidence intervals (CI) for risk assessment were calculated.
Results
Haplotype frequencies in cases vs. controls were 85.2% vs. 22.3% (DQ2.5cis), 8.3% vs. 21.6% (DQ8), and 1.2% vs. 8.2% (DQ2.2). DQ2.5 homozygosity carried the highest risk: OR 16.6 (CI 9.6-31.1), while DQ2.5/DQX had an OR of 6.3 (5.2-7.7). DQ2.5trans, although rare, still conferred a high risk (OR 10.6, 3.8-30.8). DQ8 homozygosity also posed a high risk (OR 7.5, 3.9-14.2) while DQ8/DQX had an OR of 2.1 (1.4-3.0). ORs for DQ2.2/DQ2.2 and DQ2.2/DQX were 3.0 (0.4-13.0) and 0.7 (0.3-1.3), respectively. No clear risk differences were observed between new and known cases, however, none of the new cases carried DQX/DQX in contrast to 5.6% of the known cases.
Conclusion
We found a gene-dose effect linked to DQ2.5 and DQ8 in both known and new cases, with a surprisingly high proportion of DQ8 for a Nordic population. Conversely, the large proportion of DQX/DQX in known cases compared to the absence in new cases, suggests a high prevalence of historically misdiagnosed patients.
References
1. Sollid LM (2017) The roles of MHC class II genes and post-translational modification in celiac disease. Immunogenetics 69: 605-616
2. Lukina P, Andersen IL, Eggen PT, Mjones PG, Ronne E, Bolstad N, et al. Coeliac disease in the Trondelag Health Study (HUNT), Norway, a population-based cohort of coeliac disease patients. BMJ Open. 2024;14(1):e077131.