Molecular analysis of globin gene expression in different thalassaemia disorders: individual variation of βE pre‐mRNA splicing determine disease severity

Summary Thalassaemia is characterized by the reduced or absent production of globins in the haemoglobin molecule leading to imbalanced α‐globin/non α‐globin chains. HbE, the result of a G to A mutation in codon 26 of the HBB (β‐globin) gene, activates a cryptic 5′ splice site in codon 25 leading to a reduction of correctly spliced β E ‐globin ( HBB :c.79G>A) mRNA and consequently β + ‐thalassaemia. A wide range of clinical severities in bothα‐ and β‐thalassaemia syndromes, from nearly asymptomatic to transfusion‐dependent, has been observed. The correlation between clinical heterogeneity in various genotypes of thalassaemia and the levels of globin gene expression and β E ‐globin pre‐mRNA splicing were examined using multiplex quantitative real‐time reverse transcription polymerase chain reaction (RT‐qPCR) and allele‐specific RT‐qPCR. The α‐globin/non α‐globin mRNA ratio was demonstrated to be a good indicator for disease severity among different thalassaemia disorders. However, the α‐globin/non α‐globin mRNA ratio ranged widely in β‐thalassaemia/HbE patients, with no significant difference between mild and severe phenotypes. Interestingly, the correctly to aberrantly spliced β E ‐globin mRNA ratio in 30% of mild β‐thalassaemia/HbE patients was higher than that of the severe patients. The splicing process of β E ‐globin pre‐mRNA differs among β‐thalassaemia/HbE patients and serves as one of the modifying factors for disease severity.