Pathophysiology of Thalassemia

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Title: Thalassemia

Thalassemia is a blood related genetic disorder that affects the body's ability to produce hemoglobin, a protein present in the red blood cells. People with thalassemia do not produce enough healthy hemoglobin or red blood cells in the bone marrow. Patient with alpha thalassemia does not produce enough alpha protein in the hemoglobin. Four genes, two on each chromosome 16 are needed to make alpha globin protein chains. If one of these genes is missing, it produces alpha thalassemia. The severity of thalassemia depends on how many genes are malfunctioning. Two globin genes are needed to make beta globin chains, one from each parent. If one or two of these genes are distorted, it produces beta thalassemia. Severity of beta thalassemia also depends on how many genes are mutated. Thalassemia is prevalent in populations that evolved in humid climates. The highest prevalence of alpha and beta thalassemia, the most common inherited single-gene disorders in the world, are in areas where malaria was or still is endemic.[1] There is a 25% chance with each pregnancy for an affected child. Estimate about 60-80 million people in the world carry the beta thalassemia trait alone. This is a very rough estimate and the actual number of thalassemia Major patients is unknown due to the prevalence of thalassemia in less developed countries where genetic screening resources are limited. Estimated about 1,000 people living with Thalassemia Major in the United States and an unknown number of carriers. Access to proper treatment and diagnosis can be difficult due to the prevalence of the disease in countries with less knowledge of thalassemia. [2]

One of the risk factors of thalassemia disease is family history with thalassemia. Thalassemia is passed from parents to children through mutated hemoglobin genes where there is an abnormality or mutation in one of the genes involved in hemoglobin production. This genetic defect is inherited from parents. One may develop thalassemia minor if one of the parents is a carrier for thalassemia. If this occurs, there will probably be no symptoms, but will also be a carrier of the disease. Some people with thalassemia minor do develop minor symptoms. If both parents are carriers of thalassemia, there is 25 percent chance of inheriting a more serious form of the disease. Besides that, certain ethnic groups are at greater risk in developing thalassemia. For example, alpha thalassemia most often affects people who are of Southeast Asian, Indian, Chinese, or Filipino descent and beta thalassemia most often affects people who are of Mediterranean (Greek, Italian and Middle Eastern), Asian, or African descent. [3] Thalassemia cannot be prevented because it is an inherited disease. However, it can be detected through prenatal test before birth. Family members who have thalassemia can consult a doctor if wants to have a child. They can help develop the risk of passing the disorder to the child.

Thalassemia develops when body makes an abnormal form of hemoglobin, the protein in red blood cells that carries oxygen. This blood disorder result in excessive destruction of red blood cells, which leads to anemia. Patient with alpha thalassemia does not produce enough alpha protein in the hemoglobin. Four genes, two on each chromosome 16 are needed to make alpha globin protein chains. If one of these genes is missing, it produces alpha thalassemia. The severity of thalassemia depends on how many genes are malfunctioning. Deficient production is caused by a deletion of these genes. A single gene deletion results in alpha thalassemia silent carrier status. It is asymptomatic with normal hematologic findings. [4] The two genes deletion causes alpha thalassemia trait with microcytosis but no anemia. [4] The three genes deletion results in significant production of hemoglobin H (HbH), which has four beta chains. Alpha thalassemia intermedia or HbH disease causes microcytic anemia, and hemolysis. [4] The four genes deletion results in significant production of hemoglobin Bart's have four gamma chains. Alpha thalassemia major with significant hemoglobin Bart's usually results in fatal hydrops fetalis. [4] Beta thalassemia is deficiency synthesis of beta globin chains, leading to excess alpha chains. Beta globin synthesis is restrained by one gene on each chromosome 11. The one gene defect is beta thalassemia trait (minor) and asymptomatic and results in microcytosis and mild anemia. If they are mildly anemic, their red blood cells are smaller than normal. If the synthesis from both genes is reduced or absent, the person has beta thalassemia major, known as Cooley anemia. Persons with beta thalassemia major are almost never symptomatic at birth because of the presence of HbF. [4] These symptoms begin to develop six months after birth. This condition causes life-threatening anemia that requires regular blood transfusions. If the synthesis of beta chains is mildly reduced, the person has beta thalassemia intermedia. These persons experience symptoms that are minor and have moderately severe anemia and sometimes require regular blood transfusions.

Alpha or beta thalassemia trait patients can have mild anemia. However, many people having these types of thalassemia have no signs or symptoms people with mild anemia may feel tired. Mild anemia caused by alpha thalassemia trait might be mistaken for iron-deficiency anemia. [5] People with beta thalassemia intermedia have mild to moderate anemia. They also may have other health problems. Anemia can slow down a child's growth and delay puberty. Thalassemia also causes bone marrow to expand. The spongy substance inside bones that makes blood cells is the bone marrow. The bones become wider than normal when bone marrow expands. [5] Therefore, they become brittle and break easily. Spleen is enlarged when a person has thalassemia. Spleen is an organ that helps body fight infection and remove unwanted material. The spleen has to work very hard when a person has thalassemia. [5] As a result, the spleen becomes larger than normal. This makes anemia worse. If the spleen is too large, it must be removed. People with severe thalassemia are those with hemoglobin H disease or beta thalassemia major. Signs and symptoms usually occur within the first 2 years of life. The symptoms include severe anemia and other health problems. A pale and listless appearance, poor appetite, dark urine (a sign that red blood cells are breaking down), slowed growth and delayed puberty, jaundice (a yellowish color of the skin or whites of the eyes), an enlarged spleen, liver, or heart and bone problems (especially with bones in the face). [5]

Methods of treatment for mild thalassemia are not necessary needed because signs and symptoms are usually mild with thalassemia minor and little. Occasionally, may need a blood transfusion. Some people with beta-thalassemia intermedia may need treatment for iron overload. [8] Although most people with this condition don't need the blood transfusions because people with beta-thalassemia intermedia may have increased digestive absorption of iron, leading to an excess of iron. An oral medication called deferasirox can help remove the excess iron. Treatments for moderate to severe thalassemia include frequent blood transfusions. Over time, blood transfusions cause a buildup of iron in blood, which can damage heart, liver and other organs. Patients taking this treatment may need to take medications to help get rid of extra iron in the body. However, transfusion-dependent patients develop iron overload because they have no physiologic process to remove excess iron from multiple transfusions. Therefore, they require treatment with an iron chelator starting between five and eight years of age. [8] A bone marrow transplant is also a possible cure for thalassemia patients. [9] It involves replacing affected bone marrow with bone marrow donated from a healthy donor. The new bone marrow will begin to produce healthy blood cells. However, because these procedures have high risks, including death, they're generally reserved for people with the most severe disease who have a well-matched donor available. A significant risks involved in having a bone marrow transplant is the new bone marrow can start producing cells that attack parts of body known as graft versus host disease. It can affect many parts of the body, although the eyes, skin, stomach and intestines are most commonly affected. Other risks related to bone marrow transplants include an increased risk of strokes, seizures and tumors. Splenectomy is also a method of treatment. [9] Splenectomy is a surgery to remove spleen. Thalassemia causes the enlargement of spleen. An enlarged spleen can worsen anemia. It helps reduce the number of blood transfusions needed. Gene therapy is also a cure for thalassemia patients. [10] Scientists are developing a gene therapy that may offer a cure for thalassemia. The treatment might involve inserting a normal beta globin gene into the patient's stem cells, the immature bone marrow cells that are the precursors of all other cells in the blood. Another form of gene therapy could involve using drugs or other methods to reactivate the patient's genes that produce fetal hemoglobin. Fetal hemoglobin is a form of hemoglobin found in fetuses and newborns. Lastly, a basic healthy lifestyle can help thalassemia patients. Eating a balanced diet can help thalassemia patient and is highly recommended to take supplements like folic acid. Doing physical exercise can also help thalassemia patients.

Reference

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<http://www.who.int/genomics/public/geneticdiseases/en/index2.html>

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  1. News-medical.net. 2011. Thalassemia genetic prevalence [online] Available at:

<http://www.news-medical.net/health/Thalassemia-Genetic-Prevalence.aspx> [Accessed on 31 December 2014]

  1. Familydoctor.org. Thalassemia-Causes and risk factors [online] Available at:

<http://familydoctor.org/familydoctor/en/diseases-conditions/thalassemia/causes-risk-factors.html> [Accessed on 31 December 2014]

  1. Aafp.org. 2009. Alpha and beta thalassemia [online] Available at:

<http://www.aafp.org/afp/2009/0815/p339.html> [Accessed on 31 December 2014]

  1. Nhlbi.nih.gov. 2012. What are the signs and symptoms of thalassemias? [online] Available at:

<http://www.nhlbi.nih.gov/health/health-topics/topics/thalassemia/signs>

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  1. Medicalnewstoday.com. 2014. What is thalassemia? What causes thalassemia? [online] Available at:

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  1. Healthline.com. 2012. Thalassemia [online] Available at:

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  1. Nhs.uk. 2014. Thalassemia-treatment [online] Available at:

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  1. Med.nyu.edu. 2014. Thalassemia [online] Available at:

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