A novel polymorphism causes a different restriction pattern by RsaI in the beta-globin gene cluster: application in prenatal diagnosis.

beta-Thalassemia (beta-thal) is a major health problem in Iran and the incidence of carriers is around 3-4%. The disease is caused by heterogeneous mutations in the beta-globin gene and is characterized by hypochromic microcytic anemia. The human beta-globin complex spans a region of 70 kb and contains over 20 restriction fragment length polymorphisms (RFLPs). At least nine RFLP markers including RsaI/beta in the beta-globin gene cluster have been routinely exploited for prenatal diagnosis. Here, we report a novel polymorphism upstream of the beta-globin gene characterized by RsaI digestion. Sequencing of a fragment containing this area showed a nucleotide change (T>C) at position -223 upstream of the beta-globin gene. This change could interfere with precise interpretation of the RsaI digestion pattern in linkage analysis and prenatal diagnosis of beta-thal.