important disorders

Several important disorders occur more commonly than
expected in subjects with particular HLA phenotypes, which
implies that certain HLA determinants may affect disease
susceptibility. Awareness of such associations may be helpful
in counselling. For example, ankylosing spondylitis, which has
an overall risk of recurrence of 4% in siblings, shows a strong
association with HLA-B27, and 95% of affected people are
positive for this antigen. The risk to their first degree
relatives is increased to 9% for those who are also positive for
HLA-B27 but reduced to less than 1% for those who are
negative.