In order to understand what sickle cell and Thalassaemia is one will need to understand a little of the biology of the blood, red blood cell and haemoglobin in particular.

Most of our physical characteristics are inherited through the genes we take from our parents; for example, the shape of our nose, the colour of our skin and eyes, whether we are tall or short. We also inherit our haemoglobin (Hb) type from our parents, through the genes.

The blood is made up of different parts and each part has a different function. There are red blood cells – they carry oxygen around the body, white blood cells – help the body to fight infection, platelets – clots the blood and stops bleeding and plasma – which is mainly water.

The normal red blood cell is round, soft, spongy and pliable and resembles the shape of a doughnut that has been pressed in the middle slightly. Red blood cells are made in the bone marrow and live for 120 days approximately before they get destroyed and disposed of by the body but the body is constantly making new red blood cells.

Normal Red blood Cell

The red blood cells contain a substance called haemoglobin, they are like tiny bubbles which combine with the air (oxygen) in the lungs, carry round the body to all the body parts to keep the body tissues and organs alive. Haemoglobin gives blood its red colour when it contains oxygen. These haemoglobin molecules (bubbles) stay freely flowing in the red blood cell, as illustrated in the picture below. There are different types of normal haemoglobin flowing in red blood cell, Adult haemoglobin, Fetal Haemoglobin and minor adult haemoglobin A2 (A2).

Normal Red blood Cell haemoglobin flowing freely in the red blood cell
Normal Red Blood Cells flowing through the veins

All haemoglobin is made up of a pair of globin chains and these chains are made up of amino acids, arranged in a particular sequence to make up the globin chain. The type of chain that is produced determines the type of haemoglobin that is produced:

Type of Globin Chain Fetal (F) Haemoglobin No. of Chains Adult (A) Haemoglobin No. of Chains Minor Adult Haemoglobin (A2) No. of Chains
Gamma 2 - -
Alpha 2 2 2
Beta - 2 -
Delta - - 2

It should be noted that any genetic defect affecting the alpha chains will affect the production of all these haemoglobins since all of them require a pair of alpha chains in order to produce that particular haemoglobin.

The quantity of the haemoglobin that is produced depends on the stage of human development. Fetal haemoglobin predominates whilst a baby is in the womb but it will start to make a small proportion of the adult type haemoglobin before birth. By the time a child is one year old there is a switch over in the amount of Fetal and Adult type haemoglobin produced. If a child has inherited normal haemoglobins the quantity produced at birth and throughout adulthood is indicated below:

Haemoglobin Newborn Age above one Year Old and throughout Adulthood
Haemoglobin F 95% <1%
Haemoglobin A 5 – 10% >95%
Haemoglobin A2 2.2 - 3.5% 2.2 - 3.5%

Genetic mutations (defects) of haemoglobin can affect any haemoglobin and this will determine the nature of the defect.

Click on the links below to find out about different haemoglobin types - normal haemoglobin and the most common unusual haemoglobin types.

Anyone who wants to be tested to find out which haemoglobin they have inherited from their parents can visit their GP or contact their local Specialist Centre.