Frequency of alpha-globin gene triplications and their interaction with beta-thalassemia mutations.

Our protocol for specialized diagnostics includes routine alpha-globin gene analysis for all blood samples referred to our diagnostic laboratory. alpha-Globin gene triplication is found to be present in more than 1% of samples tested. Since all cases with single alpha-gene triplications are associated with normal hematological parameters, we assume that preselection does not bias our observation and that alpha-globin gene triplications should be expected at the same frequency in the unselected Dutch multiethnic population as well. We have compared the average hematological parameters of beta-thalassemia (beta-thal) carriers with those of carriers with an associated alpha-gene triplication. In all cases, a single additional alpha gene had a very limited effect on the beta-thal minor phenotypes.