[Discordance of ankylosing spondylitis in a monozygotic twin]

In the literature the authors found reports about 18 concordant and 1 undoubtedly discordant case of ankylosing spondylitis. We describe a 34 year old male pair of twins: one of them has suffered from this disease for 12 years, while the other has had no problems. The interesting point of this case is that at present the twins are living together. Genetic problems are also discussed.