Relative numbers of human globin genes assayed with purified α and β complementary human DNA

Purified α and β globin complementary DNAs (cDNAs) have been separated from total radioactively labeled human globin cDNA using mRNA purified from liver of a hydrops fetalis (α thalassemia). The β cDNA hybridizes to the hydrops fetalis mRNA while the α cDNA remains single stranded. The purified α and β cDNAs were assayed for their purity by their hybridization to mRNA prepared from reticulocytes of nonthalassemia, α thalassemia and β thalassemia subjects. The results indicate that the separated cDNAs are selective in hybridization to α or β globin mRNAs, respectively. The previously reported deficiency of globin mRNA in thalassemia cells has been confirmed with these purified cDNAs. The purified α and β cDNAs were hybridized to cellular DNA to determine the relative number of α and β like genes in non thalassemia, β+ thalassemia and hydrops fetalis (α thalassemia DNA. The α cDNA hybridized to hydrops fetalis liver DNA to a much lower extent than β cDNA, confirming the previously reported deletion of α globin genes in hydrops fetalis. By contrast, the α and β cDNA probes hybridized to the same extent to spleen DNA from non thalassemia and from β+ thalassemia patients. Between two and five globin genes in non thalassemia and β+ thalassemia DNA hybridize to β cDNA and one to five to α cDNA. These studies indicate that in β+ thalassemia, there is no detectable deletion in β globin genes. The genetic defect in β+ thalassemia appears to be due to either repression of transcription of β globin genes or abnormal processing of β globin mRNA.