Hb Poitiers [alpha 45(CE3)His-->Asp]: a new hemoglobin variant with a two-fold increase in oxygen affinity

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.

Hb Oita [alpha45(CE3)His-->Pro]: a new silent hemoglobin variant

We describe a new alpha chain variant accidentally found in a 49-year-old female living in Usa City, Oita Prefecture, Japan. An abnormally low Hb A1c value of 2.5% (normal range: 4.8-6.3%) was found while she was treated with glucocorticoid for Fisher syndrome. The patient was also diagnosed as having an iron deficiency anemia, but otherwise showed a normal hemogram. An abnormal hemoglobin was not detectable by isoelectrofocusing and high performance liquid chromatographic methods, but appeared as a fast-moving alpha chain abnormality by urea-carboxymethyl cellulose column chromatography of the globin, from which the content of the abnormal hemoglobin was estimated at approximately 20%. The instability test of the hemolysate was normal. Structural studies demonstrated that the abnormal hemoglobin had an amino acid substitution of His-->Pro at alpha45. It is a new variant and was named Hb Oita or alpha45(CE3) His-->Pro. Additionally, sequence analysis showed a nucleotide change from A-->C at the second base in the 45th codon of the alpha2 gene, CAC(His)-->CCC (Pro). The beta/alpha ratio was 0.51 (normal range: 0.9-1.2). Her mother and a son did not have the abnormal hemoglobin variant; her father was deceased and no sample was available to verify the inheritance of the variant in this kindred.