Genetic heterogeneity in primary ankylosing spondylitis.

We studied 115 white patients suffering from primary ankylosing spondylitis (AS). HLA-B27 was present in 105 patients (92%) and 8% of controls (pc < 0.001). Four of the 10 B27 negative patients were noted to possess HLA-Bw16 (40%), compared to 3.09% of 444 B27 negative controls (pc < 0.014). These findings suggest the existence of genetic heterogeneity in primary AS. Moreover, since Bw16 is also known to be associated with psoriasis and enteropathic spondylitis, our data support the clinical suggestion that disease-susceptibility alleles for psoriasis and for chronic inflammatory bowel diseases may be important in the development of primary AS as well, even in the absence of HLA-B27.