Genetic aspects of the spondyloarthropathies.

Family studies and investigation of the HLA associations have in recent years added to our understanding of the spondyloarthropathies. In regard to ankylosing spondylitis it is likely that B27 itself is the major susceptibility gene but that additional genes may play a secondary role. Heterogeneity of the B27 antigen has been demonstrated but has not yet been shown to be relevant to disease susceptibility. Haplotypes including Cw6 are related to susceptibility to psoriasis and psoriatic arthritis and although the risk for the arthropathy is increased in B27-positive individuals, there is some uncertainty regarding the association with other B locus antigens and further work is needed. There is also uncertainty as to whether B27-associated disorders occur randomly within families, or whether particular disorders cluster in certain families and further evidence in this field would be of considerable interest. Genetic studies, as here outlined, have not as yet had a major impact in clinical medicine but it is anticipated that a deeper understanding of the mechanisms of HLA-linked susceptibility genes and in particular of how they interact with environmental agents, will improve our ability to treat and possibly prevent the relevant diseases.