Sickle cell anemia or drepanocytosis is a genetic disorder caused by mutation of a single nucleotide on the β-globin gene. As a result, the 6th amino acid, called glutamic acid is replaced by another one called valine, giving rise to mutated haemoglobin called Haemoglobin S (HbS). It is more fragile and vulnerable to destruction than normal adult haemoglobin A (HbA) and should be blamed for deformity of red blood cells (RBC) in sickle cell disease.
Haemoglobin serves as a carrier for oxygen within human body. It binds to oxygen in the lungs and then supplies it to different tissues and organs of our body. But inability of HbS to hold on to O2 creates a dearth of the gas within RBC which in turn morphs its shape from oval to a sickle one. Such a distorted shape brings forth several ruinous effects on human health.
The life span of sickle RBC is 10-12 days, as opposed to 120 days longevity of normal blood cells and its deformed contour is a complete misfit for narrow blood vessels. These imply to notable lack of RBC and haemoglobin in blood which set the stage for anaemia in near future. Several chemical shifts make the sickle RBC sticky and they get adhered to inner walls of blood vessels, jamming them in due course. Such obstructions prevent supply of oxygenated blood to tissues, much to the person’s agony. If such condition prevails, it causes severe harm to tissues and organs.
Apart from anaemia, sickle- shaped RBC also causes small blood clots, frequent urge to urinate, bloody urine, fatigue, breathlessness and unwarranted thirst. As condition becomes graver, it gives rise to frequent pangs of pain in abdomen, joints and bones owing to insufficient O2 supply to tissues. Over exertion of bone marrow in order to produce more RBC affects the normal growth of child and also calls for deferred puberty.
After collapsing, the mutated haemoglobin produces large amounts of bilirubin which in turn increases the chances for jaundice and gallstones. Impaired vision is another setback faced during sickle cell anaemia due to lack of oxygenated blood supply to the eyes. Children below age of three with sickle cell anaemia are prone to bacterial infections which can be fatal. Chest pain, stroke and other heart disorders are very common in sickle cell anaemia patients.
The autosomal recessive trait of sickle cell anaemia is of common occurrence among people with African descent. It was first detected in a 20-year old black male from West Indies by James B. Herrick in 1910. Since then, 1/3rd of all black residents of sub-Saharan Africa have been found to carry the gene for this disease. A latest WHO survey have concluded that around 2% of the child born in Nigeria have fallen victim to sickle cell anaemia totalling to 150, 000 Nigerian children being affected annually. In United States, this blood disorder has been found to distress 1 out 500 African-Americans.
Sickle cell anaemia is a genetic malady whose seed, i.e. defective β-globin gene, is spread through generations. Being autosomal recessive, this disease affects only those persons with two abnormal genes, each of maternal and paternal origin. Those with one good and one mutated “bad” gene will stay fit but have the potential to pass on the disease, and is termed the ‘carrier’. A Child of two carriers has one in four chances to develop the disease and one in two chances of being a mere carrier. Since the carrier frequency is as high as 40% in equatorial Africa, so the prevalence of sickle cell anaemia is also significant
The carrier frequency is found to have reduced to 1-2 % in North Africa and below 1% in South Africa. It is observed that HbS trait is actually a boon to inhabitants of malaria-prone areas, namely, Africa, Mediterranean and Asian countries. HbS ruptures prematurely within a carrier as a result of which the malaria parasite, which happens to dwell in RBC, cannot find a place to reproduce. Hence, a carrier of sickled RBC remains resistant to this fatal disease. If we think that nature had been foolish to select a disease to combat another disease, we should remind ourselves that malaria has caused far more deaths than sickle cell anaemia and hence the latter actually works as an advantage for the Blacks.
However, it will be erroneous to infer that blacks are the sole target of sickle cell anaemia. Apart from sub-Saharan Africa, it also rampant in other tropical regions, namely, India, Middle East as well as Mediterranean countries, such as, Greece, Italy and Turkey. The Latino-American people of Caribbean, Central American and South American origins are also troubled by this disease.
Keeping aside the genesis of sickle cell anaemia, our main focus should always be on its treatment. Refined medical vigilance controls the symptoms and ensures augmented lifespan of the affected people. Liya Das (The Caribbean Current).
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