title: Molecular and cellular analysis of a novel HBA2 mutation (HBA2: c.94A > G) shows activation of a cryptic splice site and generation of a premature termination codon.
abstract: In this study, we describe the clinical features and provide experimental analyses of a novel point mutation affecting the penultimate nucleotide of the first exon of the HBA2 (HBA2: c.94A > G) gene identified in a 26-year-old female who also carries a heterozygous Hb E (HBB: c.79G > A) variant. The aim of the study was to investigate the impact of this point mutation on the transcriptional activity of the HBA2 gene using a combination of an initial in silico prediction followed by in vitro mutagenesis and transcriptional activity assessment. The analyses revealed that the HBA2: c.94A > G point mutation causes the activation of a cryptic splice site located 49 bp upstream of the exon1-intron1 boundary in both HBA2 long and short isoforms, thus generating a frameshift and a premature termination codon between codons 48 and 49 in the second exon. A rapid degradation of the aberrantly spliced transcripts by the nonsense mediated decay (NMD) surveillance system is highly indicative of an α-thalassemia (α-thal) phenotype. However, the abnormal mRNA may not be entirely degraded since the proband presents a slight splenomegaly that could be the sign of extra vascular hemolysis.
authors.affiliation: Department of Haematology, PathWest Laboratory Medicine, Queen Elizabeth II Medical Centre , Nedlands , Western Australia .
authors.forename: Talal
authors.initials: T
authors.lastname: Qadah
authors.forename: Jill
authors.initials: J
authors.lastname: Finlayson
authors.forename: Philippe
authors.initials: P
authors.lastname: Joly
authors.forename: Reza
authors.initials: R
authors.lastname: Ghassemifar
mesh_terms: D000328:Adult; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D001483:Base Sequence; D018389:Codon, Nonsense; D004252:DNA Mutational Analysis; D004909:Erythrocyte Indices; D005091:Exons; D005260:Female; D006446:Hemoglobin E / Q000235:genetics; D006455:Hemoglobins, Abnormal / Q000235:genetics*; D006579:Heterozygote; D006801:Humans; D008969:Molecular Sequence Data; D010641:Phenotype; D017354:Point Mutation; D022821:RNA Splice Sites; D017085:alpha-Thalassemia / Q000097:blood / Q000175:diagnosis / Q000235:genetics
chemical_list: D018389:Codon, Nonsense; D006455:Hemoglobins, Abnormal; D022821:RNA Splice Sites; D006446:Hemoglobin E