- The Seronegative Spondyloarthropathies are a related family of inflammatory diseases that share certain common clinical and genetic features. The characteristic feature of these diseases is their propensity to display enthesitis or inflammation of the ligamentous attachments to bone. Nearly all individuals with spondyloarthropathies carry the HLA-B27 allele. It is important to point out that nearly 7% of the population carries the HLA-B27 and only a minor subset develop spondyloarthropathies; however, nearly all individuals with spondyloarthropathies carry the HLA-B27 allele. Finally, these diseases are termed "seronegative" because patients are typically negative for Rheumatoid Factor.