Beta Thalassemia: mutations which affect processing of the beta-Globin mRNA precursor.

To define the molecular lesion which causes decreased beta-globin synthesis in beta+ thalessemia, four patients of diverse ethnic origin were studied. Each had a 2--3 fold higher concentration of beta-globin mRNA precursor than that found in control bone marrow cells from patients with sickle cell anemia. Globin RNA metabolism was analyzed in two of these patients. Transcription of the beta-globin gene appeared to be normal, since analysis of nuclear RNA indicated that beta-globin mRNA synthesis exceeded that of alpha in a 2 hr pulse but the cytoplasm contained a relative deficiency of labeled beta-globin mRNA. An abnormal RNA species approximately 650 nucleotides in length, which contained sequences transcribed from both the large intron and coding portions of the beta-globin gene, was found in one patient's bone marrow cells. The second patient's cells contained a significant amount of a 1320 nucleotide RNA species, not initially evident in normal cells, from which part but not all of the large intervening sequence had been removed. Our data thus indicate that mutations which affect RNA processing cause beta thalessemia.