This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
HLA B27 is positive in 
Select and explain. 
A. Ankylosing spondylitis, B. Rheumatoid ahritis, C. SLE, D. Behcet syndrome
A: Ankylosing spondylitis
Answer: A: Ankylosing spondylitis 
Explanation: Ref Robbins 8/e p193; Harrison 17/e p2051 ;9/e p215 The HLA complex, which is located on the sho arm of human chromosome 6, contains sequences encoding about 100 genes, most involved in the regulation of the immune response. HLA genes are classically grouped into three major classes.