Three new neutral alpha chain variants: Hb Bois Guillaume [alpha 65(E14(Ala-->Val], Hb Mantes-la-Jolie [alpha 79(EF8)Ala-Thr], and Hb Mosella [alpha 111(G18)Ala-->Thr]

A New Hemoglobin Variant: Hb Tangshan [HBA1: c.239C > T, CD79(GCG > GTG)(Ala > Val)] Detected by MALDI-TOF MS

In this report we decribed a new α-chain variant found during the measurement of hemoglobin A1c (Hb A1c) using matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS). MALDI-TOF MS analysis detected an α-chain variant with a mass of 15,155 Da. However, this Hb variant was not detected during Hb A1c measurement by cation-exchange high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE) methods. Sanger sequencing validated the presence of a heterozygous missense mutation [HBA1: c.239C > T, CD79(GCG > GTG)(Ala > Val)]. The observed 28 Da mass difference exactly matches the theoretical mass difference (28 Da) resulting from the substitution of alanine (89.079) with valine (117.133). As this represents the initial documentation of the mutation, we named it Hb Tangshan after the proband's residence.

Hb Maruchi [α165 (E14) Ala>Pro; HBA1: c.196G>C]: A new thalassemia hemoglobinopathy related to the alpha1 globin gene

OBJECTIVE

To describe a new mutation causing alpha thalassemia and its mechanism of action.

DESIGN AND METHODS

The propositus was a 37-year-old man who presented maintained microcytosis without iron deficiency. Molecular characterization was undertaken using automatic sequencing after testing negative for the most frequent α-globin mutations by multiplex PCR followed by reverse-hybridization.

RESULTS

The mutation is a single base substitution at codon 65 of the α1 globin gene [α65(E14) Ala>Pro; HBA1: c.196G>C] and leads to the substitution of a proline residue in the E helix. The resulting hemoglobin variant has been named Hb Maruchi. This new variant cannot be separated from Hb A by electrophoretic and chromatographic techniques.

CONCLUSIONS

The substitution α65(E14) Ala>Pro; HBA1: c.196G>C causes a α-thalassemia silent associated with a very mild phenotype. The diagnosis of this type of mutation is important because it may cause alpha thalassemia if inherited with other clinically relevant HBA1/HBA2 variants.

In Silico Analysis of the Effects of Point Mutations on α-Globin: Implications for α-Thalassemia

Hemoglobinopathies are inherited diseases that impair the structure and function of the oxygen-carrying pigment hemoglobin (Hb). Adult Hb consists of two α and two β subunits. α-Thalassemia (α-thal) affects the genes that code for the α-globin chains, HBA1 and HBA2. Mutations can result in asymptomatic, mild or severe outcomes depending on several factors, such as mutation type, number of mutations and the location at which they occur. PredictSNP was used to estimate whether every possible single nucleotide polymorphism (SNP) would have a neutral or deleterious effect on the protein. These results were then used to create a plot of predicted tolerance to change for each residue in the protein. Tolerance to change was negatively correlated with the residue's sequence conservation score. The PredictSNP data were compared to clinical reports of 110 selected variants in the literature. There were 29 disagreements between the two data types. Some of these could be resolved by considering the role of the affected residue in binding other molecules. The three-dimensional structures of some of these variant proteins were modeled. These models helped explain variants which affect heme binding. We predict that where a point mutation alters a residue that is intolerant to change, is well conserved and or involved in interactions, it is likely to be associated with disease. Overall, the data from this study could be used alongside biochemical and clinical data to assess novel α-globin variants.

Characterization of a new electrophoretically silent hemoglobin variant. Hb saale OR alpha 2beta 2 84(EF8)Thr --> Ala

A new abnormal hemoglobin was detected in a young German anemic patient by cation-exchange high performance liquid chromatography (HPLC). Using a combination of electrospray mass spectrometry, HPLC, direct sequencing, and family screening with polymerase chain reaction/restriction digestion approach, we have characterized this hemoglobin variant as resulting from a Thr --> Ala replacement at beta84(EF8). It could be separated neither by electrophoresis nor by isoelectric focusing. Hb Saale is slightly unstable, exhibiting a moderate tendency to auto-oxidize. Functional properties and the heterotropic interactions are similar to those of Hb A.