Genetical factors--other than HLA-B27--in "HLA-B27-associated diseases"

All studies among acute anterior uveitis (AAU) and ankylosing spondylitis (AS) agree on the importance of and high association with HLA-B27. However, the majority (greater than 95%) of the HLA-B27+ population will never develop such disease. There are two--generally accepted--important factors increasing the relative risk for developing AAU or AS. Firstly being HLA-B27 positive and secondly being a first degree relative of a patient with AAU or AS. The association with HLA-B27 is probably based on particular HLA-B27 properties, but not on a preferential association with one of the HLA-B27 subtypes. The subtypes are equally distributed among normal controls and AAU or AS patients. Family investigations among the relatives of AAU and AS patients predict the existence of other pathogenic factors in addition to HLA-B27. Strong though circumstantial evidence for a genetical origin of these factors was found in the families. It was also found in AAU and AS family investigations that associations with other polymorphic causal genes on chromosome 6 that are in linkage disequilibrium with HLA-B27 are highly improbable.