Molecular Characterization of Alpha Thalassemia via Multiplex Ligation Dependent Probe Amplification in Konya, Turkey: A Single Center Study

ABSTRACT
Objective: Alpha thalassemia is an autosomal recessive hemoglobinopathy characterized by hypochromic microcytic anemia, exhibiting variable clinical phenotypes. Eighty-five percent of cases arise from deletions in the HBA1 or HBA2 genes. The objective of this study is to present the results of Multiplex Ligation Dependent Probe Amplification (MLPA) analysis of patients under the age of 18 with a preliminary diagnosis of alpha thalassemia.
Material and Methods: The present study examined alpha globin copy number variations determined by the MLPA method in patients who were followed up in the Pediatric Hematology department and referred to the Medical Genetics outpatient clinic with a preliminary diagnosis of alpha thalassemia between 2021-2023. We analyzed the hemogram parameters and hemoglobin electrophoresis results of the patients with deletions detected by MLPA and correlated them with their genotypes.
Results: A deletion was identified in 15 (51.7%) of 29 patients with a preliminary diagnosis of alpha thalassaemia. In eleven patients, one α-globin gene copy was deleted, while two α-globin gene copies were deleted in four patients. The most prevalent deletion was -α3.7 (36.7%), followed by -α20.5 (16.7%) and -αMED-1(6.6%). Biallelic observation of different forms of the -α3.7 deletion [-α3.7(A)/- α3.7(D), -α3.7(D) /- α3.7(F)] was noted in two cases. Additionally, one case showed biallelic -a3.7(D) deletion along with (-α)20.5 biallelic deletion, and in another case, besides -α3.7(D) deletion, a pathogenic variant p.Gly60Asp was detected in the HBA1 gene through sequence analysis.
Conclusion: Since 85% of alpha thalassemia etiology is attributed to α-globin gene deletions, the molecular genetic diagnosis rate is considerably high with MLPA analysis. In alpha thalassemia cases where MLPA analysis is normal or identified α-globin gene copy numbers that do not explain the phenotypic findings, sequencing analysis of the HBA1 and HBA2 genes should be considered.
Keywords: Alpha thalassemia, deletion, MLPA, amplification