Sickle Cell Disease and Ageing


What is Sickle Cell Disease?

Just as we inherit color of our eye and our hair from our parents, some diseases can also be inherited. Sickle cell disease is an inherited disorder or the hemoglobin in the red blood cells. Characteristics of our hemoglobin are also inherited, or passed on through the genes, from our parents.

Normal red blood cells are disc-shaped and flexible. The hemoglobin of individuals with normal red blood cells is called Hemoglobin (Hb) a. individuals with sickle cell anemia have inherited genes, that cause their red blood cell to take on the shape of a crescent or sickle when they lose oxygen to the body tissues.

Their hemoglobin is called S.

Sickle-shaped cells cannot pass easily through the small blood vessels and may result in blockage in the blood vessels. This blockage often results in painful crises and may lead to many other serious complications such as bone damage and leg ulcers’. Once the cells are sickled they become more fragile and tend to be more easily destroyed than normal cells. This means that individuals with sickle cell disease have fewer red blood cells than normal an hence have low blood level of anemia. Sickle cell disease patients may have recurrent episodes of painful crisis characterized by unbearable pains in the extremities, back, chest and abdomen. The inter-crisis period is highly variable in a given individual as well as among individuals.

What is the Sickle Cell Trait or heterozygosis?

Sickle cell trait is often confused with sickle cell anemia .In a sickle cell trait, both normal (Hb A)and sickle (Hb S) hemoglobin are present in the same red blood cells. People are the said to have “Hb AS” (an S gene is provided by one parent and A gene by the other). Approximately one in four Nigerians have sickle trait. Such person is not sick; does not have sickle cell disease and suffers from no anemia but he or she can pass the sickle cell gene on to his or her children. In population of 140 million people in Nigeria, 28 millions are carrying probable the sickle gene that are capable of passing the sickle cell genes to their children.

Sickle cell disease occurs in about 1-2% of the population so in a population of 140 million people between one to two million people would be suffering from the diseases. The diseases, as well as the control of the frequency of the disease, should be a major health undertaken in our country

How is Sickle Cell Anemia Inherited?

To have a sickle cell disease, a child must have inherited the sickle cell gene from both parents. Therefore:

Ø If one parent has sickle cell trait and the other has neither the trait nor the disease, or normal hemoglobin (AA), there is a 50 percent (two in four) chance with each pregnancy that the child will inherit the trait. The child will never have sickle cell anemia.

Ø If both parents have the trait, with each pregnancy there is a 25% chance(one in four) that a child will have the disease.

Ø If one parent has the disease (SS ) and the other has normal hemoglobin (AA), all of the children will inherit the trait (AS) none will have the disease.

Ø If one parent has the disease the other has the trait, with each pregnancy there is a 50% (two in four) chance that the child will have the disease (SS). However, we must not forget that persons with the trait do not suffer from the sickle cell disease.

How Can You Tell if a Person has the Sickle Cell Gene as a Disease or as a Trait?

For many years post-natal diagnosis of sickle cell anemia was routinely accomplished by hemoglobin electrophoresis. The hemoglobin molecule is made up of many amino acids some positively charged, some negatively charged and some carrying no charge. As a result of this, the hemoglobin molecules may have a net change in an aqueous medium. When electric field is applied to hemoglobin on a gel, the hemoglobin would move across the electric field depending on its net charge. Because the difference in charge between glutamic acid and valine which are the residues that are changed at the sixth position in the B goblin chain there is a difference in mobility between HbA and HbS. A homozygous Hbs will move slower than HbA and HbS; oo=ne corresponds to the position of Hbs and the other corresponds to the position of HbS and the other corresponds to the position of HbA. With this simple and inexpensive test is possible to examine the blood of individuals for the HbS as homozygous or as a Trait.

Professor Ogunmola and his co-worker between 1996 and 2000 conducted a screening programme for the students at the university of Ibadan over a four-year period. They screened the entire student population of about 18,000 and the distribution of the S and non-S genes in that population s is as follows: HbAA-72.16%,HbAC-3.46%,HbAS-23.28%, HbCC-0.05%,HbSC-0.53%,HbSS-0.51%. The sample population ratios are about the same as in the larger Nigerian population.