Hb Aalesund (HBA2: c.400_406delAGCACCG), an Unstable α-Globin Variant Found in a Norwegian Patient Causing Moderate Hemolytic Anemia and Falsely High Hb A1c Using Ion Exchange High Performance Liquid Chromatography

Hb Kalundborg [β79(EF3)Asp→Glu; HBB: c.240C>a], a Possible Low-affinity Hemoglobin Variant Detected during Hb A1c Measurement

A previously unknown hemoglobin (Hb) variant was detected during measurement of glycosylated Hb (Hb A_1c) after the introduction of a new high performance liquid chromatography (HPLC) apparatus. Subsequent DNA sequencing revealed a heterozygous single nucleotide substitution at codon 79 (C>A) on the β-globin gene changing an amino acid [β79(EF3)Asp→Glu; HBB: c.240C>A]. The new Hb variant was named Hb Kalundborg after the place of origin of the proband. Heterozygosity for this mutation appears to have no clinical significance in itself except for a possibly slightly lower oxygen affinity. However, it interferes with Hb A_1c measurement by HPLC, causing a falsely high Hb A_1c concentration when using the G11 apparatus with clinical implications possibly to follow.

mRNA Analysis of Frameshift Mutations with Stop Codon in the Last Exon: The Case of Hemoglobins Campania [α1 cod95 (-C)] and Sciacca [α1 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 α-globin mutants created by the deletion of a nucleotide in the penultimate or the last exon of the α1-globin gene: the Hb Campania or α1 cod95 (−C), causing a frameshift resulting in a PTC at codon 102, and the Hb Sciacca or α1 cod109 (−C), causing a frameshift and formation of a PTC at codon 133. The carriers showed α-thalassemia alterations (mild microcytosis with normal Hb A2) and lacked hemoglobin variants. The 3D model indicated the α-chain variants’ instability, due to the severe structural alterations with impairment of the chaperone alpha-hemoglobin stabilizing protein (AHSP) interaction. The qualitative and semiquantitative analyses of the α1mRNA from the reticulocytes of carriers highlighted a reduction in the variant cDNAs that constituted 34% (Hb Campania) and 15% (Hb Sciacca) of the total α1-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 no-go 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 α- and β-globin variants are available.