A subgroup of ankylosing spondylitis associated with HLA-B7 in American blacks.

In a study of 34 American black patients with primary ankylosing spondylitis, 18 were found to be HLA-B27-negative. Of these, 10 possessed HLA-B7 (55.6%) compared to 23.7% of 59 B27-negative black controls (P less than 0.025, relative risk = 4). On comparing these 10 B7-positive patients (group I) with 16 B27-positive black patients (group II), a difference in mean age at onset of disease was found: 33.6 years in group I and 22.2 years in group II (P less than 0.005). In addition, a family history of ankylosing spondylitis was absent in group I patients but present in 6 patients in group II (P = 0.034). These findings indicate an association between HLA-B7 and ankylosing spondylitis in American blacks and suggest that these patients who lack B27 but possess B7 represent a subgroup of patients with this disease.