TLR4 and ankylosing spondylitis: For ankylosing spondylitis, the most severe form of SpA with typical bone formation, a recent meta-analysis did not suggest any association of toll-like receptor 4 gene polymorphisms with susceptibility to ankylosing spondylitis [19,20], although some polymorphisms of TLR4 are linked to ankylosing spondylitis [21].