Molecular mechanism of beta-thalassaemia caused by 22-bp duplication.

A beta-thalassaemia mutation occurring from insertion of a duplicated 22-bp intron/exon junction of the beta-globin gene has been characterised. The repeated 22-bp insertion causes duplication of a 3' splice site at IVSI/exon 2 junction. Reverse transcription-polymerase chain reaction showed that the proximal 3' splice site present in the duplicated gene is used, leading to a frameshift and a premature chain termination at codon 37. beta-Globin messenger ribonucleic acid (mRNA) transcribed from the mutant gene was not detected, suggesting that the process of nonsense-mediated mRNA decay may be triggered by the premature stop codon.