Application of endonuclease mapping to the analysis and prenatal diagnosis of thalassemias caused by globin-gene deletion

We applied a recently developed and more direct technic to diagnose thalassemia syndromes associated with deletion of particular globin structural genes and to assess a fetus at risk for one of those conditions, δβ-thalassemia. The method allows assessment of the globin genes present in total cellular DNA and is applicable to amniotic-fluid cell DNA. Cellular DNA fragments produced by cleavage using two specific restriction endonucleases are separated on the basis of size by agarose-gel electrophoresis, and the distribution of specific sequences among the DNA fragments determined by molecular hybridization. We observed the total deletion of α-globin genes in homozygous α-thalassemia (hydrops fetalis with hemoglobin Bart's) and the deletion of particular β and β-like sequences in cases homozygous for hereditary persistence of fetal hemoglobin and δβ-thalassemia. Analysis of amniotic-fluid cell DNA from a fetus at risk for δβ-thalassemia demonstrated the feasibility of these improved methods for antenatal diagnosis. The molecular studies confirmed the diagnosis predicted by analysis of fetal blood and established at birth.