Phenotype of mutations in the promoter region of the β-globin gene

Abstract

Background: β⁺-Thalassaemia is characterised by reduced production of β chains, which decrease can be caused by mutations in the promoter region (CACCC or TATA box), and is classified as mild or silent depending on the extent of β-globin chain reduction. In both cases, homozygotes or compound heterozygotes for these mutations usually have thalassaemia intermedia. Frequently the diagnosis is made in adulthood or even in old age. A total of 37 alterations in the promoter region have been described so far.

Aims: In this report we describe the mutations found in the promoter region of the β-globin gene in a single hospital in Madrid.

Methods: Between 1998 and 2015, more than 9000 blood samples were analysed for full blood count and underwent haemoglobin electrophoresis and high performance liquid chromatography. Genetic analysis of the β and Gγ-globin genes was carried out by automatic sequencing and, in the case of α genes, by multiplex PCR.

Results: 35 samples showed mutation in the promoter region of the β-globin gene, with a total of six different mutations identified: one in the distal CACCC box, two in the proximal CACCC box, three in the ATA box.

Conclusions: Any alterations in the proximal CACCC and TATA boxes lead to a moderate decrease in synthesis of the β-globin chain, which has been demonstrated in cases of thalassaemia intermedia that have presented in the second decade of life with a moderate clinical course.

Keywords: MOLECULAR GENETICS; SICKLE CELL DISEASE; THALASSAEMIA.