The effects of trans-regulatory loci on globin gene control

Abstract

Augmenting the level of foetal haemoglobin (HbF) in sickle cell disease or β thalassemia patients would greatly ameliorate the symptoms associated with these diseases. This can only be achieved by first understanding the genetic switch from foetal to adult haemoglobin that is commonly referred to as γ to β globin gene switching. In this study a combination of clinical research coupled with basic research was carried out. One hundred seven β-thalassemia heterozygotes were identified by the screening program carried out by the Laboratory of Molecular Genetics, University of Malta. A complete blood count accompanied all blood samples to the laboratory. HbF and HbA2 measurements were conducted using a High- Pressure Liquid Chromatography. DNA sequencing of all samples was performed for the β globin gene and its promoter. The results showed the commonly encountered ~ thalassaemia alleles in the Maltese population; these being IVSI-6C, IVSI-llOA, Codon 39 T, IVSII-1A and other rare ones as well including a deletion of 2 nts in the β globin gene coding sequence identified for the first time in Malta. The -158 C-7T 5'Gγ globin SNP genotyping was performed by XmnI restriction enzyme digest. Three polymorphisms (rs766432, rs1l886868 and rs4671393) in BCLllA and another three (rs4895441, rs28384513 and rs9399137) in MYB were genotyped using Real Time PCR. There was a positive association between the MYB and HbF levels in β° Codon 39 heterozygotes whilst not with other β thalassaemia alleles. Only one dimorphism in BCLI1A was associated with higher HbF levels in β thalassaemia heterozygotes. As exemplified by EKLF in previous work carried out in the laboratory, and other transcription factors such as BCLIIA and MYB in this study are thought to play a significant role in promoter-specific gene activation and warrant further investigation regarding their role in globin switching.