Abstract
We identified two unstable variants in the third exon of α-globin genes: Hb Bernalda/Groene Hart (HBA1:c.358C>T), and Hb Caserta (HBA2:c.79G>A) in cis to Hb Sun Prairie (HBA2:c.391G>C), also named Hb Southern Italy. These mutations occurred in the H helix of the α-globin that is involved in heme contacting, specific recognition of α-hemoglobin-stabilizing protein (AHSP), and α1β1 interactions. The carriers showed α-thalassemia phenotype, but one also jaundice and cholelithiasis. Molecular identification of clusters of families in Southern Italy encouraged molecular characterization of mRNA, globin chain analyses, molecular modeling studies, and comparison with globin variants to understand the mechanisms causing the α-thalassemia phenotype. A normal amount of Hb Bernalda/Groene Hart mRNA were found, and molecular modeling highlighted additional H bonds with AHSP. For Hb Southern Italy, showing an unexpected α/β biosynthetic ratio typical of the β-thalassemia type, two different molecular mechanisms were shown: Reduction of the variant mRNA, likely due to the No-Go Decay for the presence of unused triplet ACG at cod 26, and protein instability due to the impairment of AHSP interaction. The UDP glucuronosyltransferase 1A (UGT1A1) genotyping was conclusive in the case of jaundice and cholelithiasis. Multiple approaches are needed to properly identify the mechanisms leading to unstable variants and the effect of a mutation.
Highlights
A growing number of unstable α-globin chain variants, in which the alteration of subunit folding renders the proteins susceptible to denaturation and proteolytic degradation, causes a deficit of α-chains similar to that characteristic of α-thalassemia mutations [1,2,3,4]
To investigate the molecular mechanism that underlies the α-thalassemia phenotype associated with Hb Southern Italy, we examined the variant both at the protein and mRNA level
We show for the first time the absence of aberrant splicing at biologically relevant levels, and by semi-quantitative analysis we demonstrated that the amount of Hb Bernalda cDNA in the reticulocytes from peripheral blood was comparable to the normal α1-globin mRNA
Summary
A growing number of unstable α-globin chain variants, in which the alteration of subunit folding renders the proteins susceptible to denaturation and proteolytic degradation, causes a deficit of α-chains similar to that characteristic of α-thalassemia mutations [1,2,3,4]. Some hemoglobins (Hbs) are destroyed so rapidly that they are undetectable in the hemolysate and for this reason are defined as hyperunstable These Hbs usually result from mutations localized in the third exon, in regions coding for the α1 β1 contacts that largely recapitulate the binding of the chaperone α-hemoglobin-stabilizing protein (AHSP) to the α-globin chain [5,6]. It is generally agreed that clinical effects are related to an abnormal protein, it is plausible that in some cases the mutation may interfere with the regulation of expression, producing aberrant mRNA that could be either inadequately processed or degraded by a mechanism of quality control [10,11] The clarification of these aspects is important in order to understand the clinical impact of the mutations, especially if found with relatively high frequency [2]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
