Celiac disease is linked to HLA-DQ2/DQ8 and causes iron deficiency through proximal small intestine malabsorption.

Celiac disease (CD) is a chronic autoimmune disorder triggered by gluten ingestion in genetically susceptible individuals. Its pathogenesis is defined by a specific genetic architecture and subsequent structural damage to the primary sites of nutrient absorption.

Genetic susceptibility and molecular mechanisms

The association between HLA-DQ2/DQ8 and celiac disease is one of the strongest known genetic links to any autoimmune condition.

• Genetic requirement: Approximately 95% of patients with CD carry HLA-DQ2, while the remaining 5% typically carry HLA-DQ8 (HLA-DQB1*03:02). These alleles are essentially required for disease development; their absence has a near-100% negative predictive value, effectively ruling out the diagnosis.
• Antigen presentation: The mechanistic role involves the HLA-DQ8 molecule’s high affinity for deamidated gluten peptides. The enzyme tissue transglutaminase 2 (TG2) deamidates glutamine residues in gluten into glutamic acid, creating a strong electrostatic fit with the HLA-DQ8 molecule.
• Immune cascade: Once these peptides are bound and presented to CD4+ T cells in the lamina propria, they trigger an inflammatory response that results in the characteristic destruction of the intestinal lining.

Pathophysiology of iron deficiency

Iron deficiency is frequently the presenting symptom of celiac disease, occurring in over 50% of newly diagnosed cases due to specific anatomical damage.

• Proximal malabsorption: Iron is primarily absorbed in the duodenum and proximal jejunum. In celiac disease, these areas are the first to encounter dietary gluten and typically sustain the most severe immune-mediated damage, known as villous atrophy (often categorized as Marsh 3 lesions).
• Cellular transport impairment: The destruction of villi significantly reduces the surface area available for nutrient uptake and impairs critical transport proteins, such as divalent metal transporter 1 (DMT1). Research indicates that iron deficiency is the leading cause of anemia in these patients, found in roughly 78.8% of those presenting with anemic symptoms.
• Recovery and persistence: While a gluten-free diet (GFD) facilitates mucosal healing, restoring iron stores can take up to two years. Some patients may experience persistent deficiency even after histological recovery due to lingering molecular alterations in enterocytes.

Bottom line

Celiac disease is fundamentally tied to the presence of HLA-DQ2 or HLA-DQ8. The disease causes iron deficiency through immune-mediated destruction of the proximal small intestinal mucosa, which directly inhibits the physiological mechanisms required for iron absorption.