Inheritance of Sickle Cell Anaemia

by NCN Health And Science Team Posted on June 19th, 2019

Today is World Sickle Cell Day. World Sickle Cell Day is a United Nation’s recognized day to raise awareness of sickle cell at a national and international level. On 22nd December 2008, the United Nations General Assembly adopted a resolution that recognizes sickle cell disease as a public health problem and “one of the world’s foremost genetic diseases.” The resolution calls for members to raise awareness of sickle cell on June 19th of each year at national and international level.

What is Sickle Cell (SCD)?

Sickle cell disorders are a group of illnesses which affect your red blood cells. Sickle cell is a genetic condition, which means it is passed on from your parents and you are born with it; you cannot catch it from other people.

Sickle cell disorders causes your normally round and flexible blood cells to become stiff and sickle shaped, stopping the blood cells, and the oxygen they carry, from being able to move freely around the body and causing pain. This can cause episodes of severe pain. These painful episodes are referred to as sickle cell crisis. They are treated with strong painkillers such as morphine to control the pain.

People with sickle cell are also at risk of complications stroke, acute chest syndrome, blindness, bone damage and priapism (a persistent, painful erection of the penis).

Over time people with sickle cell can experience damage to organs such as the liver, kidney, lungs, heart and spleen. Death can also result from complications of the disorder. Treatment of sickle cell mostly focuses on preventing and treating complications.

Did You Know?

  • SCD is inherited from both parents; sickle cell trait is inherited from one parent.
  • SCD can affect anyone, although it predominantly affects people from African and Caribbean backgrounds.
  • A simple blood test will tell whether you have sickle cell trait or the disorder
  • Children with SCD are at increased risk for stroke, the risk is highest between the ages of 2 and 16.
  • Episodes of pain may occur in sickle cell disorder and are generally referred to as a crisis
  • The only possible cure for the disorder is bone marrow transplant but this is only possible for a limited number of affected individuals who have a suitable donor. A medicine called Hydroxyurea, can significantly reduce the number of painful crises.

The Sickle Cell Trait

Sickle cell trait is inherited when only one of your parents has passed on the sickle gene, and will never develop into sickle cell disorder. You do not have symptoms from sickle cell trait, so it is a good idea to have a blood test to see if you have sickle cell trait. If you have the trait, the majority of red cells in the blood are normal round shaped cells. Some sickle shaped cells may be present under certain conditions.

The trait is not an illness, but if you are planning to have children, then certain factors have to be considered.

If your partner does not have sickle cell trait, then any children you have will not have sickle cell disorder, but they could have the trait (50% chance).

If you and your partner both have the trait, there is a 25% chance that any child conceived may have sickle cell disorder and 50% chance they will have the trait.

Inheritance of Sickle Cell Disease

Everyone has two copies of the haemoglobin gene in every cell in their body (apart from eggs and sperm). They get one from their mother and one from their father. When eggs and sperm are made, only one of the two genes goes into each egg or sperm cell. This is so that when the egg and sperm come together to make a new baby this new person has two genes in every cell in their body as well. The genes the baby gets will therefore depend on the genes carried in its parents.

Sickle Cell Anaemia is called a recessive condition because you must have two copies of the sickle haemoglobin gene to have the disorder. Sickle haemoglobin is often shortened to S or HbS. 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 you children. If your partner also has Sickle Cell Trait or Sickle Cell Anaemia your children could get Sickle Cell Anaemia.

If you know the types of haemoglobin you and your partner have, you will know the different possible combinations of genes that your baby could inherit. Only when both parents are HbAA and/or HbSS will all your children inherit the same combination of genes so you can be sure whether your child will be affected or not.

Could my Children get Sickle Cell Anaemia?

You may find the following diagrams useful to help you understand how sickle haemoglobin is inherited. In all the following diagrams you will get the same possibilities if the genes in the mother and father are swapped over.

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.

It is possible to test an unborn baby for the type of haemoglobin it has.

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.

It is possible to test an unborn baby for the type of haemoglobin it has.

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.

It is possible to test an unborn baby for the type of haemoglobin it has.

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.

It is possible to test an unborn baby for the type of haemoglobin it has.

Understanding Chance

To help you to think about chance it can be useful to use things that we are all used to. When a woman has a baby there is a one in two (50%) chance that the baby will be a girl and a one in two (50%) chance that the baby will be a boy. Although over the whole population there are almost exactly equal numbers of men and women, within any family there may be all girls, all boys or a mixture of both.

The one in two chance applies to each pregnancy afresh. The one in two chance just tells you that nature will choose one out of two different possibilities. If the chance is one in four, there are four different possibilities and the outcome will be one of these. This is very important in understanding what sort of children you will have if you carry the sickle haemoglobin gene.

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.

Symptoms of Sickle Cell

Chronic (long term) anaemia – when there are not enough red blood cells or Hb in your body.

Unpredictable Pain (crisis) – When the blood vessels get blocked, it can cause pain and swelling in the area, also known as a crisis.

You may get tired easily or experience fatigue – constant tiredness, feeling weak or lacking in energy because of the anaemia.

Jaundice – yellowing of the whites of the eyes and skin.

Living with sickle cell disease

Sickle cell disease is a life-long condition. Although the complications of sickle cell disease may not be able to be prevented entirely, living a healthy life-style can reduce some of the complications.

It is important to eat a healthy diet with lots of fruits, vegetables, whole grains, and protein, and drink lots of fluids.

Do not take decongestants because they cause constriction of blood vessels and could trigger a crisis.

Other factors that may trigger a crisis include high altitudes, cold weather, swimming in cold water, and heavy physical labor.

Avoid infections by getting an annual flu shot, washing your hands frequently, avoiding those who are sick, and getting regular dental exams.

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