HLA-B27 negative ankylosing spondylitis in a father and a son

Only 5% of AS patients are B27 negative. We describe two cases of HLA-B27 negative AS in a father and a son who both developed clinical and radiological features characteristic of AS. Tissue typing for HLA-A,-B,-C was performed in all 1.degree family members except for the father who died in 1990. All family members possessed B40. HLA-B40 may contribute to an increased susceptibility for AS not only in B27 positive individuals but also in B27 negative cases.