Table of Contents
Haemoglobin Genotype
Identifying a person’s genotype is one of the laboratory’s basic and most important tests. It is one piece of information that cannot be missing in an individual’s medical file.
Also, every human being born or yet to be born, will, at some point in his or her life, determine his or her genotype, not only for blood typing but also for other medical and social issues. It’s important to note that Genotype testing is typically performed on individuals aged two and older to minimise the interference of fetal Haemoglobin (HbF).
Depending on genetics, some Genotypes are more prevalent in certain regions than others. For instance, we see Genotypes like AA, AS, AC, and SS in West Africa.
We will soon discuss the properties that make these individual Genes different and the consequences of their identity. But first, let’s discuss how we can determine a person’s Genome.
Electrophoresis
There are various methods of Genotype determination, but today, we will explore Electrophoresis, a conventional and accessible method.
Here is how it works: Electrophoresis is a technique that separates molecules based on their sizes and charges. When an electric charge is applied, molecules migrate through the medium at different rates based on their sizes and charges. Smaller molecules will naturally migrate faster than larger molecules, and more charged molecules will migrate faster than less charged molecules.
Haemoglobin Electrophoresis
Let’s apply this to our Genotyping.
Haemoglobin is the protein that is analysed in the determination of a person’s genotype. Haemoglobin is the protein found in human red blood cells responsible for carrying the oxygen in red blood cells, from the lungs to the tissues.
Structural compositions of Haemoglobin
Different structural compositions of Haemoglobin translate to different morphologies of red cells in a thin film.
- Haemoglobin A (Hb A): this is the most common type of haemoglobin found in the human red cells.
- Haemoglobin S (Hb S): it is a variant of the normal Hb A protein. Here, a single nucleotide substitution happens in the beta globin gene, where Valine replaces Glutamic acid at the amino acid position. Because of this an abnormal Hb S tetramer is formed, that under certain conditions such a s low oxygen levels, the red cells form sickled shape. And hence reducing their capacity to carry oxygen.
- Haemoglobin C (Hb C): this is also a mutation in the beta-globin gene, but it is Lysine that substitutes Glutamic acid at the 6th amino acid position. Unlike Hb S, Hb C molecules do not sickle rather they form crystals with the red cells.
Health Implications of Abnormal Haemoglobin
Both haemoglobin S and haemoglobin C can lead to health problems, but the clinical manifestations of sickle cell disease and haemoglobin C disease are different.
Individuals with sickle cell disease experience pain crises, anaemia, splenomegaly and organ damage due to the sickling of red blood cells.
Individuals with haemoglobin C disease may have milder symptoms, such as anaemia and splenomegaly.
Common Haemoglobin Genotypes and Their Electrophoretic Migration
- AA: This genotype is considered normal and produces only normal Hb A. Hb A migrates to a specific position on the electrophoresis paper faster than the other Hb. It forms only one band as it is homozygote.
- AS: This genotype indicates the sickle cell trait. Individuals with the AS genotype produce both normal Hb A and abnormal Hb S. Hb S migrates more slowly than Hb A which is faster. both forms two bands on the paper.
- AC: This genotype is less common and is associated with a milder form of sickle cell disease. Individuals with the AC genotype produce normal Hb A and abnormal Hb C. Hb C migrates at a relatively slower rate than both Hb A and Hb S. though two bands are formed, they are much wider apart thab AS genotype as seen in the image.
- SS: This genotype indicates sickle cell disease. Individuals with the SS genotype produce only abnormal Hb S, which migrates more slowly than normal Hb A. while this also has a single band, it does not get to the point as A as shown in the image.
There are other genetic assortments like CC and SC, though they are rare, they pose health challenges as pertaining to their Haemoglobin class.
It is important therefore, for the Laboratory scientists performing these investigations using electrophoretic method, to run each sample batch with control samples (known genotypes). This will avoid the common mistakes associated with HB Genotyping.
