As an inherited genetic disorder, the onset of sickle cell anaemia requires abnormal genes to be passed from parents to their child. However, the transfer of an abnormal haemoglobin gene does not always mean that symptoms will develop, so it is important for people with sickle cell traits to understand their risk.
Sickle cell anaemia results from an abnormal haemoglobin S gene, which causes haemoglobin in the blood to be sickle-shaped (as opposed to the typical round and flexible shape). In order for a child to develop the disorder, both parents must have the irregular haemoglobin S gene, which will then be transferred to their child. In this case, the child will develop the haemoglobin SS (HbSS) form of sickle cell disease, which is associated with the most severe effects.
In the event that only one parent passes on the haemoglobin S gene, a child can experience a milder form of the disorder called haemoglobin SC (HbSC) if the other parent also passes on an abnormal haemoglobin gene (haemoglobin C) to the child. There’s also haemoglobin (HbS) beta thalassemia, which means that one parent passed along the haemoglobin S gene while the other passed on an abnormal haemoglobin beta gene.
It is important to note the difference between sickle cell anaemia and sickle cell trait. A person can carry an abnormal haemoglobin S gene without symptoms. Additionally, this person can pass along the abnormal gene to their child, but the genetic abnormality will not cause symptoms if the other parent transfers a healthy haemoglobin gene. Further research indicates that having sickle cell trait may sometimes lead to symptoms, albeit less serious ones, but severe health effects and complications are rare.