HB Chicago or alpha (2)136 (H19) Leu----Met beta 2 and a -G gamma-G gamma-globin gene arrangement in a black family

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 Bibba or alpha 2 136(H19)Leu-->Pro beta 2 in a Caucasian family from Alabama

Several members of a large Caucasian family who presented with a congenital Heinz body hemolytic anemia were found to be carriers of the unstable Hb Bibba or alpha 2 136(H19)Leu-->Pro beta 2. Identification by protein analysis was hampered by the instability of the variant which complicated its isolation from shipped blood samples. Moreover, the detection of the CTG-->CCG mutation at codon 136 of the alpha 2 gene required the substitution of dGTP by dITP during the DNA sequencing process to prevent the occurrence of secondary structures and compressions in the sequencing gel. The first Hb Bibba heterozygote, characterized in 1968 (1), is believed to be a member of this family. The clinical expression of the disease is surprisingly variable.

Hemoglobin variants in North Africa

The populations of Morocco, Algeria, and Tunisia are composed of different ethnic groups including Arabs, Berbers, Sub-Saharan Africans, Europeans, and Turks. Between 1981 and 1991, we studied more than 3,000 individuals from these North African countries. One-hundred and eighty-one carried one (or more) unusual hemoglobin variant(s) other than Hb S and Hb C which are the most frequent variants in these countries. Each of these 181 individuals was heterozygous for at least one of the 49 abnormal alpha or beta alleles identified by electrophoretic and/or structural studies, and some homozygotes were detected. A few mutants are common in North Africa: Hb O-Arab, Hb D-Punjab and Hb G-Philadelphia. Other mutants encountered in European or African populations are found in relatively few North African families. The observed polymorphisms in the populations of North Africa probably result largely from their complex ethnic origins.

Three sickle cell anemia patients each with a different alpha chain variant. Diagnostic complications

We have studied three sickle cell anemia patients who also carried a heterozygosity for one of the following alpha chain abnormalities: Hb G-Philadelphia [alpha 68(E17)Asn-->Lys], Hb Montgomery [alpha 48 (CE6)Leu-->Arg], and Hb Chicago [alpha 136(H19)Leu-->Met]. Electrophoretic analyses alone may result in incomplete and incorrect information. Confirmation of the diagnosis of Hb SS or Hb SC disease by one of the fast high performance liquid chromatographic procedures is recommended.

New results of hemoglobin variant structure determinations by fast atom bombardment mass spectrometry

Fast atom bombardment mass spectrometry has already been used for the identification of mutations in abnormal human hemoglobin chains. This paper presents new results obtained with this technique. The methodology used here is compared with more conventional biochemical techniques and automated microsequencing. In every case, a well-chosen combination of peptide-high performance liquid chromatography, mass spectrometry, amino acid analysis, and sequence analysis led rapidly to the identification of the mutant. The high sensitivity of these techniques holds great promise for the analysis of molecular abnormalities in various genetic disorders presently detectable only by the application of a molecular biological approach.

Hyperunstable hemoglobin Toyama [alpha 2 136(H19)Leu----Arg beta 2]: detection and identification by in vitro biosynthesis with radioactive amino acids

A previously reported case of congenital Heinz body anemia was reinvestigated. Heat denaturation, isopropanol testing, PCMB precipitation, isoelectricfocusing, and reversed phase high performance liquid chromatography on the red cell lysate from the patient gave either negative, or at most, questionable results. In vitro globin biosynthesis using peripheral blood with incorporation of 3H-leucine demonstrated the production of an abnormal alpha chain at the rate of about 1/3 that of the normal alpha chain. A substitution, alpha 136(H19)Leu----Arg, was elucidated by peptide mapping and radiosequencing of an abnormal tryptic peptide. The hemoglobin consisting of the abnormal alpha and normal beta chains eluted between Hb A2 and Hb A0 in anion exchange high performance liquid chromatography. It was barely detectable by this method, comprising less than 1/1000 of the amount of Hb A0, although it was produced at a level of 1/3 of that of HB A0 in terms of radioactivity. The daughter of the propositus was similarly afflicted and produced the same abnormal alpha chain. The son, who also produced the abnormal alpha chain, was essentially free from hemolytic manifestation. His red cells were microcytic and showed an alpha/beta synthetic ratio of over 2.