The entire β-globin gene cluster is deleted in a form of γδβ thalassemia

We have used restriction endonuclease mapping to study a deletion involving the β-globin gene cluster in a Mexican-American family with γδβ-thalassemia. Analysis of DNA polymorphisms demonstrated deletion of the β-globin gene from the affected chromosome. Using a DNA fragment that maps greater than 40 kilobases (kb) 5' to the ε-gene as a probe, reduced amounts of normal fragments were found in the DNA of affected family members. Similar analysis using radiolabeled DNA fragments located 3' to the β-globin cluster has shown that the deletion extends more than 17 kb 3' to the β-gene, but terminates before the 3' endpoint of the Ghanian HPFH deletion. Hence, this γδβ-thalassemia deletion eliminates over 105 kb of DNA and is the first report of a deletion of the entire β-globin gene cluster.