HLA B27 and sacroiliitis in Pima Indians--association in males only.

Since HLA B27 and ankylosing spondylitis are more common in American Indians than other Americans, the association between radiological sacroiliitis (SI) and HLA B27 was examined among the Pima Indians. SI (grade II to IV) was found in 20 per cent of randomly selected Pima adults. B27 was present in 50 per cent of males, but in only nine per cent of females with SI, vs a population frequency of 18 per cent. Among first degree relatives of probands with SI, radiologic changes were found no more frequently than in a randomly selected age matched control series. Uveitis occurred in 18 per cent of the B27 positive subjects, but in only five per cent of the B27 negative subjects (p less than 0.05). B27 was associated with SI and uveitis in Pima males, but no association was demonstrated between B27 and SI in Pima females.