The polyadenylation site mutation in the alpha-globin gene cluster

Area of Science:

• Genetics
• Molecular Biology
• Hematology

Background:

• A previous study identified a nondeletion alpha-thalassemia variant, alpha T Saudi alpha, in Saudi Arabian populations.
• Alpha-thalassemia is a genetic blood disorder affecting hemoglobin production.

Purpose of the Study:

• To elucidate the molecular basis of the alpha T Saudi alpha variant.
• To investigate the prevalence and clinical significance of this mutation in Middle Eastern and Mediterranean populations.

Main Methods:

• Synthetic oligoprobe hybridization was employed to analyze gene sequences.
• Restriction enzyme analysis was used to identify specific DNA alterations.
• Genotyping was performed to assess the presence of the mutation and associated haplotypes.

Main Results:

• The molecular cause of alpha T Saudi alpha is a single base mutation in the polyadenylation signal of the alpha 2 gene (AATAAA to AATAAG).
• A previously reported frameshift mutation in the alpha 1 gene was identified as a cloning artifact.
• The alpha 2 polyadenylation signal mutation is present in Middle Eastern and Mediterranean populations.
• This mutation contributes to Hemoglobin H (Hb H) disease in Saudi individuals with a specific five-alpha-gene arrangement (alpha T Saudi alpha/(alpha alpha alpha)T Saudi).

Conclusions:

• The identified polyadenylation signal mutation is the sole molecular cause of the alpha T Saudi alpha variant.
• This mutation is a significant factor in the pathogenesis of Hb H disease in certain populations.
• The (alpha alpha alpha)T Saudi haplotype likely resulted from chromosomal recombination involving the alpha T Saudi alpha defect.