Molecular and phenotype characterization of an elongated beta-globin variant produced by HBB:C.313delA

Introduction: beta-thalassemia is a severe hereditary hemolytic anemia. Due to the diversity of mutations spectrum, beta-thalassemia manifests a highly heterogeneous clinical severity. We noted that a previous report characterized HBB:c.313delA, at the end of exon 2, as a beta-thalassemia trait rather than dominant beta-thalassemia, the classification given to similar mutations. We further explored the impact of this functional variant on globin structure through larger pedigree analysis and in vitro studies. Methods: Hematological analysis and molecular genotyping were conducted on the proband and his family members. We evaluated functional effects of the variant on beta-globin gene in the proband's nucleated erythrocytes and transfected HEK-293T cells. Three-dimensional construction of protein structure was carried out in silico to demonstrate amino acid changes. Results: The thalassemia major proband was identified as a compound heterozygote of HBB:c.313delA and HBB:c.126_129delCTTT. Three family members with heterozygotes of HBB:c.313delA displayed microcytic hypochromic anemia. Molecular characterization demonstrated that the frameshift mutation could give rise to retro-positioning of the termination codon, resulting in an elongated beta-globin chain with an extension of 10 amino acids. Clinical phenotype and functional experiments indicated that HBB:c.313delA led to beta(0)-thalassemia phenotype. Conclusion: We concluded that the phenotype of HBB:c.313delA was mainly related to the stability of mutant mRNA, the degradation of mutant proteins, and production of inclusion bodies according to a systematic description of clinical phenotype and a series of molecular experiments.