Relative levels of alpha-, beta-, and gamma-mRNA from patients with severe and intermediate beta-thalassemia major

We have determined the relative quantities of gamma- and beta-mRNAs and the alpha/beta-mRNA ratios in 37 patients with beta-thalassemia major with specific genotypes, namely 8 with a homozygosity for codon (CD) 39 (C-->T), 7 with a homozygosity for IVS-I-110 (G-->A), 5 with a homozygosity for IVS-I-6 (T-->C), for 15 patients with compound heterozygosities for 2 of these 3 mutations, and for 2 patients with the IVS-I-110 (G-->A)/-87 (C-->G) mutations. None had an alpha-thalassemia. Twelve patients had thalassemia intermedia and the remainder, transfusion-dependent severe conditions. Differences in phenotype were observed for compound heterozygotes involving the IVS-I-6 (T-->C) mutation in combination with either the IVS-I-110 (G-->A) or the CD 39 (C-->T) mutations: patients with thalassemia intermedia had a lower alpha/beta-mRNA ratio, about half of that of the patients with severe beta-thalassemia major. This might suggest a higher beta-mRNA synthesis in some patients than in others with the same genotype; mutations in promoter, enhancer, and/or locus control region sequences may be responsible for these differences. In vitro chain synthesis data were too incomplete to be helpful in this study. The RT-PCR procedure allowed the separation of abnormal (extended) mRNA from normal beta-RNA in subjects carrying the IVS-I-110 (G-->T) mutation. The relative quantities of this beta Th-mRNA (% of beta A + beta Th) were determined by scanning of the appropriate autoradiograms; they averaged 25% for homozygotes and about 4% for heterozygotes, indicating a considerable instability of the message.