Objective: To identify a rare transcription mutation (C-->T) at position -90 of the beta-globin gene previously unreported in the beta-thalassemia carriers from a Chinese family.
Methods: In phenotype analysis, standard hematological techniques were used to measure RBC counts and Hb concentration. Reverse dot blot (RDB) analysis, which can simultaneously detect 18 known types of beta-thalassemia mutations in Chinese, was used to scan beta-globin gene mutations. DNA sequence analysis of the entire human beta-globin gene was performed to characterize the underlying causative mutation of the sample and to identify its genotype. A semi-quantitative RT-PCR method was used to measure beta-globin gene expression in the form of mRNA from the subjects.
Results: The proband, his brother and his mother presented a typical beta-thalassemic trait with reduced mean corpuscular volume (MCV, 68.2-73.6 fL) and elevated level of Hb A(2) (5.7%-6.4%) but no known beta-thalassemia mutations were found in the samples by RDB analysis. DNA sequencing of the beta-gene region of these three samples revealed heterozygosity for the C-->T substitution at position -90 within proximal CACCC box of the beta-globin gene promoter element, which was previously unreported in the Chinese population. Analysis of mRNA from the positive carriers demonstrated that the mutant beta-globin gene significantly reduced beta-globin transcription (mutants: 2.233 +/- 0.01 vs normal: 3.779+/-1.19; 95%CI: 3.060, 4.499), showing a level comparable with that of the other beta-thalassemia heterozygotes (2.110+/-0.53, 95%CI: 1.732, 2.488).
Conclusion: A rare transcriptional mutation that led to beta-thalassemia in Chinese population has been characterized. The findings enrich knowledge of the mutation spectrum of beta-thalassemia.