Does carrying HLA-DQ8 increase risk of celiac disease?

The genetic predisposition to celiac disease is highly characterized, with human leukocyte antigen (HLA) class II molecules playing a critical role in its pathogenesis.

Clinical evidence

• Elevated genetic susceptibility: HLA-DQ8 is a well-established genetic susceptibility factor for celiac disease. While it represents a weaker risk factor than the dominant HLA-DQ2.5 haplotype (which is carried by up to 90% of celiac patients), HLA-DQ8 is present in approximately 15% to 25% of individuals with the condition.
• Negative predictive value: Carriers of HLA-DQ8 have a several-fold increased risk of developing celiac disease compared to HLA-negative individuals in the general population. However, because celiac disease develops in only a small percentage of genetically predisposed individuals, the clinical utility of HLA testing lies primarily in its exceptional negative predictive value. The absence of both HLA-DQ2 and HLA-DQ8 makes a diagnosis of celiac disease highly unlikely, with an exclusion rate exceeding 99%.

Mechanistic explanations

• Antigen presentation pathway: The molecular mechanism of HLA-DQ8-mediated susceptibility centers on antigen presentation in the intestinal mucosa. Partially digested gluten fragments persist as immunogenic peptides.
• Deamidation by transglutaminase 2 (TG2): In the lamina propria, the enzyme TG2 deamidates specific neutral glutamine residues within these peptides, converting them into negatively charged glutamate residues.
• T-cell activation: This modification significantly increases the binding affinity of the gluten peptides to the HLA-DQ8 heterodimer, which favors negatively charged anchors. The resulting HLA-DQ8-peptide complex is presented on antigen-presenting cells to gluten-specific CD4+ T cells, triggering the inflammatory cascade that drives enteropathy.

Bottom line

• Carrying the HLA-DQ8 allele significantly increases the genetic risk of developing celiac disease by facilitating the presentation of deamidated gluten peptides to CD4+ T cells, although its presence is a predisposing factor rather than a direct guarantee of disease onset.