Haemoglobin S - Sickle Cell

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.

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).

The type of haemoglobin gene which a person has inherited from their parents determines the type of Adult haemoglobin they will have. Genes always come in pairs one from the mother and one from the father. Therefore, every individual inherits two Adult Haemoglobin genes.

The normal and most common haemoglobin gene combination that an individual can inherit from their parents is Haemoglobin AA (Hb AA).

Worldwide some people inherit unusual haemoglobins from their parents, for example, Sickle Cell Haemoglobin (S), which is one of over 1000 unusual haemoglobins found in humans and is a defect of the beta chain.

Sickle and other unusual haemoglobins are most common among people whose ancestors originate from former and current malaria zones of the world; for example Africa, Asia, the Middle and Far East, Mediterranean islands, and South America. Because of migration and intermarriage, it is also seen in people who did not originate from malaria zones of the world including White Northern Europeans.

Sickle Cell Trait

Where a person has inherited haemoglobin A from one parent and sickle haemoglobin S from the other, they have Sickle Cell trait, commonly written Hb AS; this individual is considered a ‘healthy carrier’. The person with sickle cell trait does not have an illness, are not likely to experience any symptoms and his or her health is not affected; this is why a person with sickle cell trait will not know that they carry this unusual haemoglobin unless they have had a special blood test or when they have a child who is later found to have sickle cell disease.

It has been reported that some people with sickle cell trait have problems concentrating their urine therefore they may get dehydrated, especially when the weather is very hot or they are sweating a lot and have not drunk enough water. This may also make them prone to getting urine infections especially women during pregnancy. Because of this people with sickle cell trait should, like everyone else, make sure they drink plenty of water and if they get any signs of urine infection such as a burning sensation when they pass water they must see their doctor promptly and get treatment with antibiotics.

  • 1 in every 10 African-Caribbean,
  • 1 in every 4 West Africans,
  • 1 in every 50 Asians,
  • 1 in every 100 Northern Greeks, have sickle cell trait.

Many athletic people have sickle cell trait and it does not affect their physical performance in any way. In normal day to day living conditions the red blood cells of people with Sickle Cell trait (Hb AS) is the same shape and has the same ability to carry oxygen just as well as a normal red blood cell.

Importance of Sickle Cell Trait

Although sickle cell trait does not affect the carrier in any way, it is important for them to know that they have this unusual haemoglobin because in the same way that they inherited one haemoglobin A from one of their parents and a sickle haemoglobin S from the other, their children will inherit one haemoglobin from them and the other haemoglobin from their partner. Sickle cell trait cannot change into any other form of haemoglobin trait or disease later in life.

Sickle cell trait is also important if a person needs to have general anaesthetic for any operation including dental treatment. A person with sickle cell trait may need special care during the operation and the person managing the anaesthetic need to be aware of this.

If a couple are both Carriers (trait) of sickle cell or any other unusual haemoglobin combination

If a couple both have sickle cell trait or one of them has inherited another unusual haemoglobin combination there is a chance that their child can inherit sickle cell disease. To work out how inheritance works see Inheritance of Haemoglobin.

The couple’s children will inherit whichever haemoglobin the parents pass on to the child. Apart from sickle cell haemoglobin there several other unusual haemoglobin genes which if combined with the sickle cell haemoglobin gene can lead to any one of a number of conditions called Sickle Cell Disease collectively but the most common and often the most serious of these is Sickle Cell Anaemia (Hb SS).

Sickle Cell Anaemia

Sickled Red Blood Cells

If a person inherits sickle haemoglobin from both parents they have sickle cell anaemia (Hb SS), which is one of a group of conditions collectively called sickle cell disease (SCD). Red blood cells which contain mainly sickle haemoglobin lose their ability to keep the round, soft, spongy shape and texture of a normal red blood cell. The sickle haemoglobin inside the red blood cells stick together forming long stiff rods inside the red blood cell causing it to become hard, rigid, brittle and to assume the shape of a farmer’s sickle (banana shaped), as illustrated below.

SCD causes a moderate to severe anaemia (pale blood). Sometimes the sickled red blood cells clog together in the blood circulation and cause a blockage in blood flow leading to a severe pain called a ‘sickle crisis pain’. For further information see Sickle Cell Disease.

The Family Connection

Once Haemoglobin S or any other unusual haemoglobin gene has been found in one family member it is important to be aware that other members of the same family may also have the unusual haemoglobin gene. Therefore, it is important to share the information with other family members especially with those who are of child bearing age, planning to get married, start a family or have more children - brother, sisters, aunts, uncles, cousins.

Testing for Sickle Cell

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 National Sickle Cell / Thalassaemia Centre.