Sickle Cell Disease

Hip hop fans around the world are presently mourning the death of Prodigy, one half of popular  hip hop duo known as Mobb Deep. He died at the age of 42 due to complications from sickle cell disease.

This coming just a few days after the world marked Sickle cell awareness day (19th June) A day set aside to create awareness about Sickle cell disease) has brought this dreaded illness into focus recently.

If you are from Nigeria, chances are you’ve most likely heard about sickle cell before, maybe you even know a “sickler”. However not many people really understand what the disease is about and how it occurs.

Sickle cell is an inherited disease. This means that it is not a condition that is caused by any external factors, it is caused by genetic material which are passed from parent to offspring.

It is actually a group of disorders, with the most common type being sickle cell anemia.

Sickle cell is a hematological disorder. This means that it has to do with blood.

Blood is made up of a compound called hemoglobin. This Hemoglobin has 4 subunits, and in people with sickle cell disease, at least one of the subunits in hemoglobin is replaced with hemoglobin S. In sickle cell anemia, hemoglobin S replaces two subunits in hemoglobin resulting in HbSS.

In other types of sickle cell disease, just one subunit in hemoglobin is replaced with hemoglobin S. The other subunit is replaced with a different abnormal variant, such as hemoglobin C. For example, people with sickle-hemoglobin C (HbSC) disease have hemoglobin molecules with hemoglobin S and hemoglobin C and this usually results in a milder form of the disease.

Normal red blood cells are flexible and round, moving easily through your blood vessels. In sickle cell anemia, the red blood cells become rigid and sticky and have a crescent moon shape. This irregular shape causes the cells to get stuck in small blood vessels, which can slow or block blood flow and oxygen to parts of the body. It is this reduction in supply of oxygen to parts of the body that usually manifests as the painful crises which are typical of sickle cell disease.

The pattern of inheritance for sickle cell disease is Autosomal recessive because you must have two copies of the sickle haemoglobin gene to have the disorder.

If you have only one copy of the sickle haemoglobin along with one copy of the more usual haemoglobin (A or HbA) you are said to have Sickle Cell Trait. This is not an illness but means that you “carry” the gene and can pass it on to your children. Two partners who have Sickle Cell Trait or Sickle Cell Anaemia may give birth to children with Sickle Cell Anaemia.

A simple blood test (hemoglobin electrophoresis) can tell you what your genotype is.

If one parent has sickle cell trait (HbAS) and the other does not carry the sickle haemoglobin at all (HbAA) then none of the children will have sickle cell anaemia. There is a one in two (50%) chance that any given child will get one copy of the HbS gene and therefore have the sickle cell trait. It is equally likely that any given child will get two HbA genes and be completely unaffected.

If both parents have sickle cell trait (HbAS) there is a one in four (25%) chance that any given child could be born with sickle cell anaemia. There is also a one in four chance that any given child could be completely unaffected. There is a one in two (50%) chance that any given child will get the sickle cell trait.

If one parent has sickle cell trait (HbAS) and the other has sickle cell anaemia (HbSS) there is a one in two(50%) chance that any given child will get sickle cell trait and a one in two chance that any given child will get sickle cell anaemia. No children will be completely unaffected.

If one parent has sickle cell anaemia (HbSS) and the other is completely unaffected (HbAA) then all the children will have sickle cell trait. None will have sickle cell anaemia. The parent who has sickle cell anaemia (HbSS) can only pass the sickle haemoglobin gene to each of their children.

From my experience, it appears many people believe that when two people with sickle cell decide to have children, 50% of their offspring would be affected and the other 50% would not. So if they have 4 children then two may be affected but the other two will not.

However this is not the case. For example, if there is a one in four chance that you will have a baby with sickle cell anaemia, and if you go on to have a number of children, it is still possible that all your children could have sickle cell anaemia or that none will have sickle cell anaemia.

This is why it is important to first know your genotype and that of your partner and undergo professional genetic counselling prior to having children.