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 B 27 is not seen in which of the following 
Select and explain. 
A. Ankylosing spondylitis, B. Reiter's syndrome, C. Rheumatoid ahritis, D. Psoriatic ahritis
C: Rheumatoid ahritis
Answer: C: Rheumatoid ahritis 
Explanation: Ref Robbins 9/e p215 HLA and diseases, the association of B27 with ankylosing spondylitis (AS) is the strongest. The B27 antigen is present in over 90% of patients with AS as com- pared with the B27 prevalence of 8% in Caucasians in general. A strong but slightly minor association has also been found between B27 and Reiter's syndrome (RS), reactive ahritis (ReA), and acute anterior uveitis (AAU). It is negative in rheumatoid ahritis