The present study was performed on 61
HLA-B27 positive first-degree relatives and 40
HLA-B27 negative relatives of 20
HLA-B27 positive probands with
ankylosing spondylitis (AS). Of 24
HLA-B27 positive relatives 45 years or older, 21% had AS and 38%
sacroiliitis. The
HLA-B27 negative relatives did not have features of either disease. In the population study of 2,957 individuals 45 years or older, we found 5 cases of
HLA-B27 positive
sacroiliitis (according to the New York criteria) and 3 of these fulfilled the New York criteria for diagnosis of AS. In 2 of these 3 individuals, the diagnosis was made on clinical grounds. The phenotype frequency of
HLA-B27 in this population is 7.8%, or about 230
HLA-B27 positive individuals in this population sample. Since AS was found in only 3 individuals, 1.3% of the
HLA-B27 positive individuals in the population at large have AS; therefore, our data show that among individuals 45 years or older, 21% of
HLA-B27 positive relatives of
HLA-B27 positive AS patients have AS as compared with 1.3% of the
HLA-B27 positive individuals in the population at large. Thus, the risk for AS is 16 times greater in the
HLA-B27 positive relatives compared with
HLA-B27 positive individuals in the population at large. The discriminatory value of the New York criterion of history of
pain or the presence of
pain at the dorsolumbar junction or in the lumbar spine was analyzed in the population and family studies and was found to be too nonspecific.