alpha-Thalassemia Associated with Hb Instability: A Tale of Two Features. The Case of Hb Rogliano or alpha1 Cod 108(G15)Thr->Asn and Hb Policoro or alpha2 Cod 124(H7)Ser->Pro.

We identified two new variants in the third exon of the alpha-globin gene in families from southern Italy: the Hb Rogliano, alpha1 cod108 ACC>AAC or alpha1[alpha108(G15)Thr->Asn] and the Hb Policoro, alpha2 cod124 TCC>CCC or alpha2[alpha124(H7)Ser->Pro]. The carriers showed mild alpha-thalassemia phenotype and abnormal hemoglobin stability features. These mutations occurred in the G and H helices of the alpha-globin both involved in the specific recognition of AHSP and alpha1 chain. Molecular characterization of mRNA, globin chain analyses and molecular modelling studies were carried out to highlight the mechanisms causing the alpha-thalassemia phenotype. The results demonstrated that the alha-thalassemia defect associated with the two Hb variants originated by different defects. Hb Rogliano showed an intrinsic instability of the tetramer due to anomalous intra- and inter-chain interactions suggesting that the variant chain is normally synthesized and complexed with AHSP but rapidly degraded because it is unable to form the alpha1beta1 dimers. On the contrary in the case of Hb Policoro two different molecular mechanisms were shown: the reduction of the variant mRNA level by an unclear mechanism and the protein instability due to impairment of AHSP interaction. These data highlighted that multiple approaches, including mRNA quantification, are needed to properly identify the mechanisms leading to the alpha-thalassemia defect. Elucidation of the specific mechanism leads to the definition of a given phenotype providing important guidance for the diagnosis of unstable variants.