HLA‑DQ2 and HLA‑DQ8 are specific HLA class II molecules (encoded by HLA‑DQA1/DQB1 genes) that present gluten-derived peptides to CD4+ T cells. They strongly predispose to celiac disease: most people with celiac carry DQ2 or DQ8, but carriage alone isn’t sufficient for disease. Their absence makes celiac disease very unlikely.

HLA‑DQ2 and DQ8 are strongly linked to celiac disease (most patients carry DQ2; others DQ8) and its extraintestinal forms—dermatitis herpetiformis and gluten ataxia. They also raise risk for type 1 diabetes and are overrepresented in other autoimmune conditions, especially autoimmune thyroid disease and some autoimmune liver disorders. Presence of these alleles is a risk marker but not diagnostic on its own.

Four key markers used to diagnose celiac disease are: 1) anti–tissue transglutaminase antibodies (tTG‑IgA); 2) anti‑endomysial antibodies (EMA‑IgA); 3) deamidated gliadin peptide antibodies (DGP IgA/IgG); and 4) characteristic duodenal biopsy findings (villous atrophy, crypt hyperplasia). Total IgA and HLA‑DQ2/DQ8 typing may be used adjunctively. These markers guide diagnosis alongside symptoms and gluten exposure.

Celiac disease is strongly associated with HLA class II molecules, primarily HLA‑DQ2 and, less commonly, HLA‑DQ8. HLA‑DQ2 (mainly DQA1*05 with DQB1*02) is present in about 90–95% of patients; HLA‑DQ8 (DQA1*03 with DQB1*03:02) accounts for most remaining cases. HLA typing has high negative predictive value—absence of these alleles makes celiac disease unlikely.

Most people with celiac disease carry HLA‑DQ2 or HLA‑DQ8—roughly 95% have DQ2 and most of the remainder DQ8. If both alleles are absent, celiac becomes very unlikely and genetic testing is often used to exclude the diagnosis. Rare exceptions exist, so clinical context, serology and intestinal biopsy remain important; HLA testing helps when other results are inconclusive.

There are two main types of celiac disease: classical (typical) celiac, characterized by intestinal malabsorption symptoms such as chronic diarrhoea, weight loss, bloating and nutrient deficiencies; and non‑classical (atypical or extraintestinal) celiac, which presents with extraintestinal features like iron‑deficiency anaemia, fatigue, osteoporosis, neurological symptoms or subtle GI complaints; both require a gluten‑free diet.