A Previously Undescribed β+ Thalassemia Mutation (HBB:c.-122T>A) Identified in a Vietnamese Family

Aims: To identify thalassemias in the population living in the Thua Thien Hue Province of Central
Vietnam.
Study Design: The study was performed as part of an ongoing research collaboration between
Universities of Sassari and Hue. The survey included nearly 200 individuals referred to Hue Medicine
and Pharmacy College and PhuVang District Hospitals for hematological and clinical evaluation. Firstlevel
analysis and DNA studies were carried out to identify and define thalassemia defects.
Methodology: Complete blood count was measured. Serum ferritin concentration was used to
determine irondeficiency.
Hemoglobin profile was defined by IEF and CEHPLC
procedures.
Identification of the βglobin
genotype was carried out by PCR and nucleotide sequencing of the βglobin
gene. The occurrence of deletions or duplications in the HBB and HBA cluster was investigated
by the Multiplex LigationDependent
Probe Amplification (MLPA) analysis. To assess the impact of a
novel mutation on globin synthesis a K562 cellbased
luciferase reporter assay was performed.
Results: Four βglobin
gene mutations were found, three of which previously described. The
unknown mutation affects the position 72
from the Cap site, located in the CCAAT box of the β
promoter region. The variant is not associated with remarkable changes in red blood cells indices.
The level of HbA2 is slightly increased. The in vitro expression studies displayed that the mutation
decreases the transcriptional activity of the β promoter by about 50%. This finding made possible to
classify the mutation as a β+thalassemic
allele.
Conclusions: Although the mildness of the 72
mutation a severe phenotype resulting from a
compound heterozygous state cannot be excluded. The complexity of the clinical manifestations
resulting from the assortment of different β thalassemia alleles underlines the importance of
identifying new or rare β+thalassemic
alleles, particularly in countries where a wide genetic variability
exists.