Реферат: Sickle Cell Disease Essay Research Paper The

Sickle Cell Disease Essay, Research Paper

The sickle cell disease is an inherited blood disorder that affects red blood

cells. People with sickle cell have red blood cells that have mostly

hemoglobin’s, Sometimes these red blood cells become sickle-shaped or crescent

shaped and have trouble going through small blood vessels. When sickle-shaped

cells block small blood vessels, less blood can get to that part of the body.

Tissue that does not get a normal blood flow eventually becomes damaged. This is

what causes the problems of sickle cell disease. As to this day there is really

no cure for sickle cell disease. Red blood cells take oxygen from the air we

breathe into our lungs to all parts of the body. Oxygen is carried in red blood

cells by a substance called hemoglobin (Hemoglobin? is the main substance of

the red blood cell. It helps red blood cells carry oxygen from the air in our

lungs to all parts of the body). Normal red blood cells contain hemoglobin A.

Hemoglobin S and hemoglobin C are abnormal types of hemoglobin. Oxygen is

carried in red blood cells by a substance called hemoglobin. The main hemoglobin

in normal red blood cells is hemoglobin A. Normal red blood cells are soft and

round and can squeeze through tiny blood tubes (vessels). Normally, red blood

cells live for about 120 days before new ones replace them. People with sickle

cell conditions make a different form of hemoglobin A called hemoglobin S (S

stands for sickle). Red blood cells containing mostly hemoglobin S do not live

as long as normal red blood cells (normally about 16 days). They also become

stiff, distorted in shape and have difficulty passing through the body’s small

blood vessels. When sickle-shaped cells block small blood vessels, less blood

can get to that part of the body. Tissue that does not receive a normal blood

flow eventually becomes damaged. This is what causes the complications of sickle

cell disease. There are several types of sickle cell disease. The most common

are: Sickle Cell Anemia (SS), Sickle-Hemoglobin C Disease (SC) Sickle Beta-Plus

Thalassemia and Sickle Beta-Zero Thalassemia. Sickle Cell trait (AS) is an

inherited condition in which both hemoglobin A and S are made in the red blood

cells, there are always more A than S. Sickle cell trait is not a type of sickle

cell disease. People with sickle cell trait are generally healthy. Sickle cell

conditions are inherited from parents in much the same way as blood type, hair

color and texture, eye color and other physical things. The types of hemoglobin

a person makes in the red blood cells depend upon what hemoglobin genes the

person inherits from his or her parents. Like most genes, hemoglobin genes are

inherited in two sets?one from each parent (Ex. If one parent has Sickle Cell

Anemia and the other is Normal, all of the children will have sickle cell trait.

4 If one parent has sickle cell anemia and the other has sickle cell trait,

there is a 50% chance (or 1 out of 2) of having a baby with either sickle cell

disease or sickle cell trait with each pregnancy, When both parents have sickle

cell trait, they have a 25% chance (1 of 4) of having a baby with sickle cell

disease with each pregnancy). HOW DO YOU KNOW IF YOU HAVE THIS TRAIT A SIMPLE

PAINLESS BLOOD TEST followed by a laboratory technique called Hemoglobin

Electrophoresis will determine the type of hemoglobin you have. When you pass an

electric charge through a solution of hemoglobin, distinct hemoglobins move

different distances, depending on their composition. This technique

differentiates between normal hemoglobin (A), Sickle hemoglobin (S), and other

different kinds of hemoglobin (such as C, D, E,). Medical Problems Sickle cells

are destroyed rapidly in the body of people with the disease causing anemia,

jaundice and the formation of gallstones. The sickle cells also block the flow

of blood through vessels resulting in lung tissue damage (acute chest syndrome),

pain episodes (arms, legs, chest and abdomen), stroke and priapism (painful

prolonged erection). It also causes damage to most organs including the spleen,

kidneys and liver. Damage to the spleen makes sickle cell disease patients,

especially young children, easily overwhelmed by certain bacterial infections.

TREATMENT Health maintenance for patients with sickle cell disease starts with

early diagnosis, preferably in the newborn period and includes penicillin

prophylaxis, vaccination against pneumococcus bacteria and folic acid

supplementation. Treatment of complications often includes antibiotics, pain

management, intravenous fluids, blood transfusion and surgery all backed by

psychosocial support. Like all patients with chronic disease patients are best

managed in a comprehensive multi-disciplinary program of care. Promising

Treatment Developments In search for a substance that can prevent red blood

cells from sickling without causing harm to other parts of the body, hydroxyurea

was found to reduce the frequency of severe pain, acute chest syndrome and the

need for blood transfusions in adult patients with sickle cell disease.

Hydroxyurea is a well-known drug, however its use in sickle cell disease is

relatively new and must be approached with caution. Short-term side effects must

be carefully monitored and long-term effects are still unknown POTENTIAL SAVINGS

FROM USE OF HYDROXYUREA Estimated total U.S. sickle cell patients 65,000.

Percent with severe pain 3-5 times per year 5.2%. Estimated number with frequent

severe pain 3,380. Assuming the average annual number of episodes 4. The total

number of severe pain episodes in these patients 13,520. Assuming that 50%

episodes result in hospitalization 6,760. Assuming the average days of

hospitalization 5. Estimated total number of hospital days for these patients

33,800. Assuming cost per day $800. Total hospitalization costs for these

patients $27,040,000. Potential savings from use of hydroxyurea in these

patients in one year $13,520,000. Estimates of sickle cell disease patients in

the U.S. is now over 70,000. In the US there were approximately 65,000

African-Americans suffering from sickle-cell disease. There were about 5,500

British sufferers. Worldwide, 100,000 babies are born with the disease annually.

Sickle cell anemia results when a person inherits two genes for sickle

hemoglobin, and is homozygous for the mutation. American-Africans are the most

likly to develope sickle cell anemia. Hemoglobin is composed of two pairs of

peptide chains: two alpha chains and two beta chains. Sickle hemoglobin results

from a point mutation in the beta-globin gene. This single nucleotide change

produces a single amino acid change: a glutamic acid at position 6 has been

changed to a valine, according to the following schedule. COOH \ CH —

(CH2)2-COOH Glutamic acid / NH2 COOH CH3 \ | CH – CH-CH3 Valine / NH2 Glutamic

acid is, as the name says, an acidic amino acid, which means it will have a

negative charge under normal body conditions and thus likes to be surrounded by

water molecules. Valine, on the other hand, is a neutral, or uncharged, amino

acid. Under normal conditions it behaves like a hydrophobic, organic molecule

and wants to hide from water. This difference makes the globin chains of

hemoglobin fold differently, especially in the absence of oxygen. Normal

hemoglobin just gives up its oxygen when it gets to the tissue that needs it,

but it retains its shape. Sickle hemoglobin, on the other hand, loses its

oxygen, and becomes relatively insoluble. In the deoxygenated form, it forms

into long arrays that come out the shape of the red cell and produce the

characteristic sickling that characterizes the disease. The insolubility of

deoxygenated (reduced) sickle hemoglobin is the basis of two rapid diagnostic

laboratory tests for sickle cell anemia. Scientists recently have had some

limited success in using genetic engineering techniques to get good copies of

the beta globin gene into people with sickle cell anemia. If they can succeed in

this endeavor, people with the disease may be cured but will still be able to

pass the genes onto their offspring.


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