Segregation of HL-A27 and ankylosing spondylitis in an informative kindred.

A family with high prevalence of ankylosing spondylitis (A.S.) was investigated for the presence of HL-A27. In this family, classical A.S. occurred in five subjects and possible A.S. in two out of 64 members examined. In all seven cases, HL-A27 was present. The study of the segregation of A.S. and HL-A27 in this kindred demonstrates that more than one gene is responsible for the expression of A.S., that the homozygous state for the HL-A27 gene may lead to the occurrence of A.S., and that possibly a simple genetic explanation accounts for the simultaneous transmission of HL-A27 and A.S.