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

Int J Lab Hematol. 2021 Dec;43(6):1620-1627. doi: 10.1111/ijlh.13639. Epub 2021 Jul 16.

Abstract

Introduction: β-thalassemia is a severe hereditary hemolytic anemia. Due to the diversity of mutations spectrum, β-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 β-thalassemia trait rather than dominant β-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 β-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 β-globin chain with an extension of 10 amino acids. Clinical phenotype and functional experiments indicated that HBB:c.313delA led to β0 -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.

Keywords: HBB; clinical heterogeneity; elongated β-globin chain; frameshift mutation; β0-thalassemia.

MeSH terms

  • Alleles*
  • Amino Acid Substitution
  • Erythrocyte Indices
  • Erythrocytes / metabolism
  • Erythrocytes / pathology
  • Exons
  • Frameshift Mutation
  • Genetic Association Studies
  • Genetic Predisposition to Disease
  • Genetic Testing
  • Genotype
  • Heterozygote
  • Humans
  • Inclusion Bodies
  • Phenotype*
  • Sequence Deletion*
  • beta-Globins / genetics*
  • beta-Thalassemia / blood*
  • beta-Thalassemia / diagnosis
  • beta-Thalassemia / genetics*

Substances

  • beta-Globins