Familial aggregation of ankylosing spondylitis in Southern China.

OBJECTIVE: To study the familial aggregation of ankylosing spondylitis (AS) in southern China and to compare the clinical and laboratory characteristics between the probands and their first-degree relatives with AS. METHODS: On the basis of questionnaires to 473 patients with AS, 402 responded and 36 self-reported having first-degree relatives with symptoms related to spondyloarthropathies. All together, 144 of 150 first-degree relatives of these 36 probands were examined for clinical and radiographic characteristics. HLA typing for HLA-B27 was performed by standard microlymphocytotoxicity method. RESULTS: The disease duration of the 36 probands was 5.03 +/- 3.76 years (0.5-14 yrs). Forty seven first-degree relatives of the 36 probands were diagnosed as having AS. The prevalence of AS among the first-degree relatives of these 36 aggregated families was 31.3%. The overall prevalence of AS among the first-degree relatives in these 402 families was estimated to be 2.8%. The recurrence risk of the first-degree relatives within these aggregated families was 31.3%, suggesting an excess risk to them of 120.4, while it was 10.8 to the general families. The probands more often had peripheral arthritis and enthesopathies (p < 0.001 and p = 0.01, respectively) than the AS patients among the first-degree relatives. HLA-B27 was associated with development of AS in the probands and the patients among the first-degree relatives. CONCLUSION: Although familial aggregation of AS in southern China is uncommon in general, the recurrence risk of the first-degree relatives of AS probands within the aggregated families is extremely high, according to our study among hospital based patients. As the disease of the first-degree relatives is often mild and atypical, familial background analysis should be encouraged to assist early diagnosis.