Hemoglobinopathy

Hemoglobinopathy is the medical term for a group of blood disorders and diseases that affect red blood cells.
It can be a kind of genetic defect that results in abnormal structure of one of the globin chains of the hemoglobin molecule. Hemoglobinopathies are inherited single-gene disorders; in most cases, they are inherited as autosomal co-dominant traits. Common hemoglobinopathies include sickle-cell disease. It is estimated that 7% of world's population (420 million) are carriers, with 60% of total and 70% pathological being in Africa. Hemoglobinopathies are most common in populations from Africa, the Mediterranean basin and Southeast Asia.
Hemoglobinopathies are simply structural abnormalities in the globin proteins themselves. Thalassemias, in contrast, usually result in underproduction of normal globin proteins, often through mutations in regulatory genes. The two conditions may overlap, however, since some conditions which cause abnormalities in globin proteins (hemoglobinopathy) also affect their production (thalassemia). Thus, some hemoglobinopathies are also thalassemias, but most are not.
Either hemoglobinopathy or thalassemia, or both, may cause anemia. Some well-known hemoglobin variants such as sickle-cell anemia and congenital dyserythropoietic anemia are responsible for diseases, and are considered hemoglobinopathies. However, many hemoglobin variants do not cause pathology or anemia, and thus are often not classed as hemoglobinopathies, because they are not considered pathologies. Hemoglobin variants are a part of the normal embryonic and fetal development, but may also be pathologic mutant forms of hemoglobin in a population, caused by variations in genetics. Other variants cause no detectable pathology, and are thus considered non-pathological variants.
Migration patterns.
Alkaline electrophoresis.
In general on alkaline electrophoresis in order of increasing mobility are hemoglobins A2, E=O=C, G=D=S=Lepore, F, A, K, J, Bart's, N, I, and H.
In general a sickling test (sodium bisulfite) is performed on abnormal hemoglobins migrating in the S location to see if the red cells precipitate in solution.
Acid electrophoresis.
In general on acid electrophoresis in order of increasing mobility are hemoglobins F, A=D=G=E=O=Lepore, S, and C.
This is how abnormal hemoglobin variants are isolated and identified using these two methods. For example, a Hgb G-Philadelphia would migrate with S on alkaline electrophoresis and would migrate with A on acid electrophoresis, respectively
use of iso electric focusing to determine quantitative differences in globin chain synthesis and high performance liquid chromatography that separates hemoglobins based on their various affinities for the column
Classification of Hemoglobinopathies.
A) Qualitative.
Structural abnormalities.
Hb variants: Hb structural variants are qualitative defects that cause a change in the structure (primary, secondary, tertiary, and/or quaternary) of the Hb molecule. The majority of Hb variants do not cause disease and are most commonly discovered either incidentally or through newborn screening. A subset of Hb variants can cause severe disease when inherited in the homozygous or compound heterozygous state in combination with another structural variant or a thalassemia mutation. When clinical consequences occur, they may include anemia due to hemolysis or polycythemia due to alterations in the oxygen affinity of the abnormal Hb. Common examples of hemoglobin variants associated with hemolysis include sickle Hb (Hb S) and Hb C. Hb variants can usually be detected by protein-based assay methods; however, DNA-based methods may be required for variants with ambiguous or unusual results from protein analysis.
The major functional consequences of Hb structural variants can be classified as follows:
Globin chains: Many of the clinically important hemoglobinopathies are caused by missense mutations in the coding sequence of a globin gene (single nucleotide substitutions that alter the amino acid sequence of the resulting protein).
Haeme
2. Unstable Hb:
B) Quantitative
Amount abnormalities.
Copy number variation (e.g., deletion, duplication, insertion) is also a common genetic cause of Hb disorders, and complex rearrangements and globin gene fusions can also occur.
Hemoglobin variants.
Haemoglobin variant are not necessarily pathological. For example, haemoglobin Valletta and haemoglobin Marseille are two haemoglobin variants which are non-pathological
Evolution.
Some hemoglobinopathies (and also related diseases like glucose-6-phosphate dehydrogenase deficiency) seem to have given an evolutionary benefit, especially to heterozygotes, in areas where malaria is endemic. Malaria parasites live inside red blood cells, but subtly disturb normal cellular function. In patients predisposed for rapid clearance of red blood cells, this may lead to early destruction of cells infected with the parasite and increased chance of survival for the carrier of the trait.
Hemoglobin functions:
Pathology and organic structural abnormalities may lead to any of the following disease processes:
Hemoglobin Biology.
Normal hemoglobins — Human Hbs are tetrameric proteins composed of two pairs of globin chains, each of which contains one alpha-like (α-like) chain and one beta-like (β-like) chain. Each globin chain is associated with an iron-containing heme moiety. Throughout life, the synthesis of the alpha-like and the beta-like (also called non-alpha-like) chains is balanced so that their ratio is relatively constant and there is no excess of either type.
The specific alpha and beta-like chains that are incorporated into Hb are highly regulated during development: