Comparison of two known chromosomal rearrangements in the δβ-globin complex with identical DNA breakpoints but causing different Hb A(2) levels.

We report three cases with very heterogeneous Hb A(2) levels caused by known chromosomal rearrangements in the β-globin locus. These rearrangements had their breakpoints at the same region in the δ gene, leading either to the Senegalese δ(0)β(+)-thalassemia (δ(0)β(+)-thal) deletion or to an insertion of a δ gene, known as Anti-Lepore. One patient showed, apart from drastically increased Hb A(2) values of 17.0%, inconspicuous hematological values. He had an Anti-Lepore mutation with three copies of the δ gene, thus explaining the high Hb A(2) level. Two other patients had Hb A(2) levels in the lower borderline range and increased Hb F levels. Molecular analysis showed the Senegalese δ(0)β(+)-thal deletion. One of them presented with an additional mild β-thal mutation leading to β-thal intermedia. These cases illustrate that different gene rearrangements with the same breakpoints in the δ gene can lead to different levels of Hb A(2) depending on the remaining number of δ genes.