mRNA analysis of frameshift mutations with stop codon in the last exon: The case of hemoglobins Campania [alpha1 cod95 (-C)] and Sciacca [alpha1 cod109 (-C)]

An insertion or deletion of a nucleotide (nt) in the penultimate or the last exon can result in a frameshift and premature termination codon (PTC), giving rise to an unstable protein variant, showing a dominant phenotype. We described two ?-globin mutants created by the deletion of a nucleotide in the penultimate or the last exon of the alpha1-globin gene: the Hb Campania or alpha1 cod95 (-C), causing a frameshift resulting in a PTC at codon 102, and the Hb Sciacca or alpha1 cod109 (-C), causing a frameshift and formation of a PTC at codon 133. The carriers showed alpha-thalassemia alterations (mild microcytosis with normal Hb A2) and lacked hemoglobin variants. The 3D model indicated the alpha-chain variants' instability, due to the severe structural alterations with impairment of the chaperone alpha-hemoglobin stabilizing protein (AHSP) interaction. The qualitative and semi-quantitative analyses of the alpha1mRNA from the reticulocytes of carriers highlighted a reduction in the variant cDNAs that constituted 34% (Hb Campania) and 15% (Hb Sciacca) of the total alpha1-globin cDNA, respectively. We developed a workflow for the in silico analysis of mechanisms triggering no-go decay, and its results suggested that the reduction in the variant mRNA was likely due to nogo decay caused by the presence of a rare triplet, and, in the case of Hb Sciacca, also by the mRNA's secondary structure variation. It would be interesting to correlate the phenotype with the quantity of other frameshift mRNA variants, but very few data concerning alpha-and beta-globin variants are available.