Genotypes - AA,AS,AC,SS. Know Your Compatibility!

Last Tuesday, the 19th of June was the international sickle cell day.
On that day, I took time out to ask random people about their genotype and what they know about sickle cell anaemia. Most people “think” they have a certain genotype, others are not sure of that of their partners.

The term sickle cell disease (SCD) describes a group of inherited red blood cell disorders. People with SCD have abnormal haemoglobin( Haemoglobin is a protein in red blood cells that carries oxygen throughout the body),called hemoglobin S or sickle hemoglobin, in their red blood cells.
“Inherited” means that the disease is passed by genes from parents to their children.
SCD is not contagious. A person cannot catch it, like a cold or infection, from someone else.

People who have SCD inherit two abnormal hemoglobin genes, one from each parent. In all forms of SCD, at least one of the two abnormal genes causes a person’s body to make hemoglobin S. When a person has two hemoglobin S genes, Hemoglobin SS, the disease is called sickle cell anemia. This is the most common and often most severe kind of SCD.


With sickle cell disease, red blood cells contort into a sickle shape. The cells die early, leaving a shortage of healthy red blood cells (sickle cell anaemia) and can block blood flow causing pain (sickle cell crisis).
Infections, pain and fatigue are symptoms of sickle cell disease.





When the hemoglobin S gene is inherited from only one parent and a normal hemoglobin A gene is inherited from the other, a person will have sickle cell trait, AS. People with sickle cell trait are generally healthy.
Only rarely do people with sickle cell trait have complications similar to those seen in people with SCD. But people with sickle cell trait (AS) are carriers of a defective hemoglobin S gene. So, they can pass it on when they have a child.
If the child’s other parent also has sickle cell trait (AS) or another abnormal hemoglobin gene (like thalassemia, hemoglobin C, hemoglobin D, hemoglobin E), that child has a chance of having SCD.


Study this table below carefully:
AA + AA = AA, AA, AA, AA
AA + AS = AA, AS, AA, AS,
AA + SS = AS, AS, AS, AS,
AA + AC = AA, AA, AA, AC,
AS + AS = AA, AS, AS, SS,
AS + SS = AS, SS, SS, SS,
AS + AC = AA, AC, AS,SC,
SS + SS = SS, SS, SS, SS,
AC + SS = AS, AS, SS, SC,
AC + AC = AA, AC, AC, CC,

 Based on the table above, you can see that a person with the genotype AA can marry across. There’s no risk of having a sicklier for a child even when he or she marries an SS.
Someone with the genotype AS should only marry someone with the genotype AA because if AS marries another AS there’s one out of 4 chances (AS, AS, AA and SS) that they will have a child with the sickle-cell disease.
Same applies when AC is combined. AC and AS combine will produce AA, AS, AC, SC, the sickle-cell disease will be SC.
Of course there are many cases where two abnormal was combined that is an AS and AS or AC and AC or AC and AS couples and had up to five or six children without a single sicklier among them. But there is no need to risk it!
SC, SS, or CC are Sickle cell diseases.

 The symptoms of sickle cell-haemoglobin C disease are less severe than the symptoms of sickle cell disease. The main difference between SS and SC is the symptoms caused by each genotype.
Treatments include medication, blood transfusions and rarely a bone-marrow transplant.
People who do not know whether they carry an abnormal hemoglobin gene can ask their doctor to have their blood tested.
Couples who are planning to have children and know that they are at risk of having a child with sickle cell disease (SCD) may want to meet with counsellor.

Do have a wonderful week!

Pharm G B. IDAMKUE


Reference:

1. Hearing impairment in persons with the hemoglobin SC  genotype. Accessed here on 22nd of June, 2018
2.Diffference between SS and SC genotype. Accessed here on 22nd of June, 2018.
3. Sickle Cell Disease. National Heart, Lung and Blood Institute. Accessed here on 23rd of June, 2018.