HLA antigens are encoded for by genes on chromosome 6. HLA A, B and C are class I antigens whilst DP, DQ, DR are class II antigens. Questions are often based around which diseases have strong HLA associations. The most important associations are listed below:

A3

• primary hemachromatosis (B14) HFE gene

B51

• Behçet’s disease

B8

• Graves' disease, Celiac sprue/ Dermatitis Herpitiformis, Primary sclerosing cholangitis (A1, B8 and DR3)

B27  'PAIR'

• Psoriatic arthritis, Postgonococcal arthritis,
• Ankylosing spndylitis, Acute anterior uveitis,
• Inflammatory bowel,
• Reactive Arthritis (Reiter's $)

B47

• 21-hydroxylase deficiency

DQ2, DQ8

• celiac disease

DRB1

• Mixed connective tissue disease (MCTD), Autoimmune hepatitis,
• RA ((DRB104:01 and DRB104:04 hence the association with DR4)

DR2