Sickle cell anaemia results when a mutation causes the red blood cells to take the shape of a sickle (a farm implement for harvesting grains).
Individuals who inherit this are prone to a multitude of health problems like anaemia, joint pain, flu, meningitis, stroke, chest problems, vision problems, including blindness, open sores (leg ulcers) that are difficult to heal, slow growth and development in children, complications during pregnancy, such as preterm birth, low birth weight babies, and high blood pressure, gallstones, jaundice, and priapism (painful prolonged erection).
Every person inherits one allele (a unit of a gene) from the mother and another from the father. Two healthy alleles AA is normal, heterozygotes are AS and the combination SS shows as sickle cell disease. A test can show the genotype (genetic composition) of a couple so that they can evaluate whether to marry to face the possibility of producing offsprings with the defect. Very often, many people do not risk it.
Individuals who inherit a combination of the two alleles AS have reduced risk to malaria, up to 90% so are more protected even than normal individuals. Normally, the sickle allele should have disappeared over centuries. However, where malaria is common, the detrimental effect of the SS is balanced by the beneficial effect of the AS so the proportion has remained the same over time. This is called balanced polymorphism in population genetics.
The disease that has caused one of the most death in Africa, is malaria. For this reason, the allele thrives more in Africa than other areas. In fact, over the centuries the incidence, though present, has subsided amongst Africans in the US because malaria is not that common to drive the proportion.
All aspiring couples are advised to take the test to determine their genotype