Hb Foggia or alpha 117(GH5)Phe -> Ser: a new alpha 2 globin allele affecting the alpha Hb-AHSP interaction

We report a novel α2-globin gene allele with the mutation cod 117 TTC>TCC or α117(GH5)Phe>Ser detected in three carriers with α-thalassemia phenotype. The mutated mRNA was present in the reticulocytes in the same amount as the normal one, but no chain or hemoglobin variant were detected. Most likely the amino acid substitution impairs the interaction of the α-chain variant with the AHSP and prevents its stabilizing effect, thus leading to the α-chain pool reductio

Identification and molecular characterization of a novel 55 kb deletion recurrent in Southern Italy: the Italian (G) γ((A) γδβ)°-thalassemia

OBJECTIVES: To characterize the molecular basis of a β-thalassemia defect in subjects with mild microcytosis associated with normal Hb A2 and increased levels of Hb F. METHODS: Six subjects from 3 apparently unrelated families from Campania (Southern Italy) have been investigated by using DNA restriction analysis, Inverse PCR, cloning, sequencing, Multiplex ligation-dependent probe amplification (MLPA), quantitative Real Time PCR, gap-PCR. RESULTS: We have identified a novel 55 kb β-globin gene cluster deletion in three unrelated families: the Italian (G) γ((A) γδβ)°-thalassemia. This deletion removes most of β-globin cluster. The 5' breakpoint was within the (A) γ-globin exon 2 and the 3' breakpoint was within a 160 bp palindrome: the breakpoint-flanking regions present a micro-homology (5'-TGGG-3') that, together with the palindromic structure, may have contributed to the recombination. CONCLUSIONS: Large deletions of β-globin gene cluster are usually found in single families. Here we report about the novel Italian (G) γ((A) γδβ)°-thalassemia we have found in three families. Twenty years ago the characterization of the first family was challenging, whereas that of the other families has taken advantage of nowadays techniques. The relatively high frequency of this novel deletion in Southern Italy suggests that it should be tested, together with the Sicilian (δβ)°-thalassemia, in Italian and Mediterranean families with microcytosis, normal Hb A2 and increased Hb F levels

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 α-globin gene in families from southern Italy: the Hb Rogliano, α1 cod108 ACC>AAC or α1[α108(G15)Thr→Asn] and the Hb Policoro, α2 cod124 TCC>CCC or α2[α124(H7)Ser→Pro]. The carriers showed mild α-thalassemia phenotype and abnormal hemoglobin stability features. These mutations occurred in the G and H helices of the α-globin both involved in the specific recognition of AHSP and β1 chain. Molecular characterization of mRNA, globin chain analyses and molecular modelling studies were carried out to highlight the mechanisms causing the α-thalassemia phenotype. The results demonstrated that the α-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 α1β1 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 α-thalassemia defect. Elucidation of the specific mechanism leads to the definition of a given phenotype providing important guidance for the diagnosis of unstable variants

HbA2-Partinico or δ(A2)Pro→Thr, a new genetic variation in the δ-globin gene to the β thal IVS-I-110 G>A, and the heterogeneity of δ-globin alleles in double heterozygotes for β- and δ-globin gene defects

International audienceThe study of the alleles of the δ-globin gene is relevant to the prevention of β-thalassemia homozygosis; in fact, the increase of the HbA2 is an invaluable hematological marker of the β-thalassemia heterozygosis and the double heterozygosis for alleles of δ- and β-globin genes can cause the decrease of the HbA2 up to normal or borderline values. We carried out the characterization of alleles of the δ- and β-globin genes, restriction fragment length polymorphism (RFLP) haplotype background, and hematologic phenotype in 23 double heterozygotes belonging to 18 unrelated families. A wide heterogeneity of the δ-globin alleles was detected; seven known alleles to the β-globin gene defects were revealed in 17 out of 18 families, while a new allele to a β-thalassemia allele was detected in one family. Moreover, the relative frequency of the δ-mutants was quite different from that found among heterozygotes. The new allele δ-cod 5 CCT>ACT, to the allele β thal IVS-I-110 G>A, was found in five carriers of a Sicilian family. The new variant δ5(A2)Pro→Thr, named HbA2-Partinico upon the origin of the family, was detected with high-performance liquid chromatography; it overlapped the HbA2 peak which was partially split. The double heterozygotes had increased percentage of normal and variant HbA2 of comparable size. The variant originated most likely from a new mutational event because it was associated with RFLP haplotype I, commonly found with the β thal IVS-I-110 G>A, even if crossing over or gene conversion cannot be excluded