Sickle cell disease (SCD), also known as sickle cell anemia is seen mostly in Sub-Saharan Africa. SCD is an inherited/genetic condition that affects the hemoglobin (oxygen-carrying) molecules within red cells. Sickle Cell Disease is a recessive inherited condition; this means you must have two copies of the sickle hemoglobin gene to have the disorder, one from your mother and one from your father.
But a person who receives a gene for sickle cell disease from one parent and a normal gene from the other has a condition called “sickle cell trait.” Sickle cell trait produces no symptoms or problems for most people; it is not an illness but means that you “carry” the gene and can pass it on to your children. If your spouse also has Sickle Cell Trait or Sickle Cell Disease, it means your children could get Sickle Cell Disease. Note; Sickle cell disease is not contagious neither can it be passed on to another person.
SCD is a chronic disorder marked by the tendency of hemoglobin molecules within red cells to become sticky and deform. When this happens, the red cell becomes a sickle (or crescent) shape resulting in blockage of blood vessels and accelerates the breakdown of red blood cells.
The genes involved in sickle cell disease, control the production of hemoglobin in red blood cells. Hemoglobin binds oxygen in the lungs and delivers it to the peripheral tissues, such as the liver and muscles. Poor oxygen delivery to organs is the primary cause of symptoms and complications.
There is a high prevalence of SCD in sub-Saharan Africa; this is attributed to survival advantage conferred by the sickle cell trait against Plasmodium falciparum. The resistance of individuals with sickle cell trait to Plasmodium falciparum creates a selective pressure that has maintained the sickle cell gene within human populations in malaria endemic regions like sub-Saharan Africa.
The level of severity of sickle cell disease varies tremendously; some individuals lead lives that are nearly normal. While others are less fortunate, and can suffer from a variety of complications. The recurrent pain and complications caused by the disease can interfere with many aspects of the patient’s life, including education, employment, and psychosocial development.
Can the SCD gene change over time?
No, the sickle cell genes cannot change over time, but the severity of the disease can vary over time. The difference in severity is not due to a change in the sickle cell genes rather, some biological and environmental factors, change to alter the severity of sickle cell disease. In the same vein, individuals with sickle cell trait will always have sickle cell trait; they cannot change to develop sickle cell disease as they grow older. People with sickle cell traits rarely develop problems related to their single sickle cell gene, and then only under very unusual conditions.
Inheritance of Sickle Cell Disease
As mentioned earlier, sickle cell disease is a recessive inherited condition; both parents most have the abnormal gene. If both parents carry the sickle cell trait, then for each pregnancy, there is a one-in-four (25%) chance that a child will inherit two normal genes from the parents. In that same pregnancy, there is also a one-in-four chance that a child will inherit two sickle cell genes, and have sickle cell disease. Or a one-in-two (50%) chance that the child will inherit a normal gene from one parent and a sickle gene from the other and carry a sickle cell trait.
It is paramount to bear in mind that each time this couple has a child, the chances/probability of that child having sickle cell disease remain the same. That is, if the first-born baby has sickle cell disease, there is still a 25 percent chance that the second, third, fourth or fifth, etc. child will also have the disease. Both boys and girls can inherit sickle cell trait, sickle cell disease, or normal hemoglobin. The one in four chance applies to each pregnancy afresh; this just tells you that nature will choose one out of four different possibilities.
In summary, if there is a one in four chance that you will have a baby with sickle cell disease and if you go on to have many children, it is still possible that all your children could have sickle cell disease or that none will have sickle cell disease. These probabilities occur for each child independently of what happened with earlier/prior children the couple may have had. This probability invariably means that each new child has a one-in-four chance of having sickle cell disease.
A couple with sickle cell trait can have eight children, none of whom have two sickle genes. Another couple with sickle trait can have two children each with sickle cell disease. The inheritance of sickle cell genes is purely a matter of chance. These probability odds cannot be altered or changed.
If you know the types of hemoglobin you and your partner have, you will know the different possible combinations of genes that your baby could inherit. You may find the diagram below useful to help you understand how sickle hemoglobin is inherited. In all the following pictures you will get the same possibilities if the genes in the mother and father are swapped over.
The lines coming in to each baby show that one gene has come from the mother, and one gene has come from the father. In these diagrams, the presence of the normal hemoglobin gene is shown by pink and the presence of the sickle hemoglobin gene is indicated by blue.
One parent has sickle cell trait (HbAS) while the other does not carry the sickle hemoglobin at all (HbAA) then none of the children will have sickle cell disease. In this case, 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.
One parent has sickle cell trait (HbAS), and the other has sickle cell anemia (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 disease. No children will be completely unaffected.
One parent has sickle cell anemia (HbSS), and the other is completely unaffected (HbAA) then all the children will have sickle cell trait. None will have sickle cell disease. The parent who has sickle cell disease (HbSS) can only pass the sickle hemoglobin gene to each of their children.
If a child’s other parent also has sickle cell trait or another abnormal hemoglobin gene (like thalassemia, hemoglobin C, hemoglobin D, hemoglobin E), that child has a chance of having SCD.
Factors Other Than The Sickle Genes that also Influence Sickle Cell Disease
Sickle cell disease is quite variable in itself. Factors that contribute to this variability are unknown; the few known ones include genetics and environmental influences. One of the most important genetic factors is thalassemia. One form of thalassemia called beta -thalassemia, reduces the production of normal hemoglobin.
If one parent has sickle cell trait, and the other have thalassemia trait, any child they conceive has one chance in four of receiving one gene for sickle cell disease and one gene for beta-thalassemia
This condition is called sickle beta-thalassemia, and the severity varies. Some patients with sickle beta-thalassemia have a health condition as severe as sickle cell disease itself, while others have few and relatively mild problems.
Another hemoglobin disorder is hemoglobin C; this abnormal hemoglobin C protein is relatively harmless. But individuals with two hemoglobin C genes have a relatively mild clinical condition termed “hemoglobin C disease”. When hemoglobin C combines with hemoglobin S, it produces “hemoglobin SC disease”. Usually, hemoglobin SC disease is milder than sickle cell disease. However, some patients with hemoglobin SC disease have a clinical condition as severe as any with sickle cell disease and the reason for the marked variability is unknown.
Sickle cell disease is an unfortunate occurrence caused by decisions that can somewhat be avoided by parents. The best solution is prevention. Primary prevention involves preventing the disease before it even happens by creating awareness, genetic counseling to couples about to marry and general public knowledge. If it has already occurred, early detection and screening help reduce morbidity and mortality. Medicines and vaccines are used for chemoprophylaxis, and adequate clinical care of special groups (children, pregnant women).
Secondary and tertiary prevention of complications, involves physiotherapy, lifestyle management, appropriate pain management, social support, improve the quality of life of patients and build partnerships whether online or onsite.
Thank you for reading this article. Your questions are welcome.
Wishing you good health and happiness,
Dr Nse Onyebuchi