Phenotype And Molecular Characterization Of An Elongated β-globin Variant Produced By HBB:c.313delA

Background and Objectivesβ-thalassemia（β-thal）is a severe hereditary hemolytic anemia with abundant mutation spectrum.Due to the diversity of mutations and modifiers,the clinical phenotype of β-thal appears high heterogeneity.We noted that a previous report of HBB:c.313del A at the end of exon 2 was classified in β-thalassemia trait rather than dominant β-thal of other reported similar mutations.In-vitro validations were carried out to explore the impact of the functional variant on globin structure.Participants and methodsWe firstly collected the haematological indices of the proband and his family members.Multiple molecular tests,including NGS,Gap-PCR and Sanger Sequencing were carried out upon the proband and family members for genotypic characterization.We evaluated the functional effects of the pathogenic variant on HBB RNA and protein level in proband’s nucleated erythrocytes and mutant transfected HEK-293T cells.Three-dimensional construction of protein structure in-silico have been done to demonstrate amino acid changes.ResultsThe thalassemia major proband was identified to be a compound heterozygote of HBB:c.313delA（p.Arg104GlyfsTer54）and HBB:c.126₁29delCTTT.The family members who are heterozygotes of HBB:c.313del displayed microcytic hypochromic anemia.Molecular characterization demonstrated the frameshift mutation can give rise to a retroposition of termination codon,resulting in an elongated β-globin chain with an extension of 10 amino acids.Clinical phenotype and functional experiments indicated that the β-thal mutation HBB:c.313delA led to β0-thal phenotype.ConclusionWe attempted to expound the relationship between phenotype and genotype in HBB:c.313delA with more systematically clinical phenotype and a series of molecular experiments.We concluded that the phenotype of frameshift mutations mapping at exon 3 or the end of exon 2 are usually related to the synthesis of mutant mRNA,the degradation of mutant proteins and production of inclusion bodies.