Mutations in Distal Cis-Regulatory Elements in the Beta Globin (HBB) Gene Promoter of Filipinos Influences Transcriptional Activity.

Background/

Objectives

Hemoglobin is a component of the red blood cell responsible for carrying oxygen. It is composed of four chains, two of each for the alpha and beta globin. Mutations in the gene, beta-globin (HBB), coding for the beta-globin chains causes beta-thalassemia. Common diagnostic methods for this genetic disorder cover only the coding region of the HBB gene.

Methods

Cis-regulatory elements within the distal HBB promoter region were predicted in silico. Promoter variants were identified through PCR amplification and Sanger sequencing, while HBB gene expression was assessed. Hematologic parameters were measured, and associations between promoter variants, gene expression, and hematologic parameters were statistically analyzed.

Results

Sequencing showed varying mutations in the predicted cis-regulatory elements which suggests less binding of transcription factors leading to a potential change in HBB gene activity. This is corroborated by the gene expression analysis where the presence of more mutations in the promoter region resulted in a higher downregulation of the HBB gene which manifested in hematologic analysis as lower mean corpuscular volume (MCV) and hemoglobin (HGB). Among the cis-regulatory element mutations that potentially explain the reduced expression in HBB are binding to transcription factors such as TATA and GATA.

Conclusions

Our work illuminates the importance of expanding analysis of beta-globin variations to the promoter region for understanding the causes of thalassemia traits that cannot be explained by conventional diagnostic methods to employ appropriate treatment strategies.