HLA B27 and ankylosing spondylitis: a population and family study in Sardinia.

Thirty-eight patients with ankylosing spondylitis (AS) and 494 unrelated controls in Sardinia were HLA Typed. HLA B27 was present in 81.8 per cent of AS vs 5.3 per cent of controls (relative risk: 80). Twenty-six apparently healthy B27 positive individuals were studied clinically and radiologically, and six (23.0 per cent) presented signs of definite or suspicious AS. A family study on relatives of seven AS B27-positive and four AS B27-negative patients was also made. The results suggest a dominant heredity of AS susceptibility, and are compatible with a direct involvement of the B27 antigen in the mechanism of AS, but we cannot rule out a closely linked disease-susceptibility gene with incomplete penetrance.