Genetic Disorder- Thalassemia

by : Deepa Prem



Genetic Disorder- Thalassemia

Thalassemia is a hereditary disease. It is an autosomal recessive blood disease. Autosomal recessive pattern means both copies of the gene in each cell have mutations. Thalassemia is also known as Mediterranean anemia, Jaksch anemia or Cooley's anemia. This is not a single disorder but a group of defects with similar clinical effects. A group of inherited anemia, in which there is a defect in alpha or beta chains of hemoglobin. The anemia affected to the alpha chains is known as alpha thalassemia and the anemia affected to the beta chains are called beta chains. Thalassemia major is to describe homozygote and Thalassemia minor to heterozygote. The defect results in reduced rate of synthesis of one of the globin chain that makeup hemoglobin. This causes the formation of abnormal hemoglobin molecules which causes anemia, a characteristic symptom of thalassemias. Thalassemia includes different types of anemia. The severity depends up on the number of genes it affected. In this disorder the patient is unable to produce red blood cells and the reduction has to be supplemented with the transfusion of red blood cells, every 2-3 weeks to make patient healthy and to survive.

Alpha Thalassemia

It is caused by a decrease in the production of alpha globin chains due to mutation of the genes in the hemoglobin molecule. On each number sixteenth chromosome there two alpha globin chains can be seen forming a total number of four. In fetal hemoglobin which is made before birth and in hemoglobin A and hemoglobin A2 which is present after birth, the alpha chain is an important component. Alpha thalassemia in a parent can be identified mostly after the birth of an effective child. The most severe form of alpha thalassemia causes still birth. There are four types of thalassemia.
Alpha thalassemia carrier or silent carrier: Carrier is carrying the genes but does not have symptoms and there is no need of treatment for carriers. In carriers two alpha chain genes are deleted i.e. both from the same number 16 chromosome are deleted known as
'Cis deletion' and one each from the number 16 chromosomes are deleted known as 'trans deletion'. If the parents are the carriers of 'cis deletion', there are 25 percent of chances of having a baby with alpha thalassemia major with each pregnancy. Only by DNA analysis, the carriers of both deletions can be distinguished.
Hemoglobin H disease: This occurs when a person has only one functioning alpha chain gene, resulting in hemolytic anemia which means three alpha chain genes are deleted. Persons with this disorder are at a risk to have a child of alpha thalassemia major as they carry one number sixteen chromosome with cis deletion.
Alpha thalassemic major: This condition results in the death of the fetus in the uterus because all the four alpha chain genes are deleted here.
Hemoglobin H-constant spring: This more acute than the hemoglobin H disease. Patients have severed anemia and frequently suffer from the enlargement of spleen and other viral infections.
Alpha thalassemia is commonly found in countries like Africa, Middle East, India, South East Asia, and Southern China and in Mediterranean region. Carriers of this disease can be determined by the following tests:
(a)Complete blood change (CBC): This is the measurement of size, number and maturity of different cells in a specific volume of blood.
(b)Hemoglobin electrophoresis with A2 and F quantition: This is a lab procedure that differentiates the types of hemoglobin present in the blood.
(c)FEP (Free Erythrocyte protoporphyrin) and Ferritin: This is to exclude iron deficiency anemia.
These tests can be performed from a single blood sample. Prenatal (before birth) diagnosis can perform by taking sample from chorionic villus.
Treatment of alpha thalassemia depends on numerous factors. They are:
(a)Child's age, health and medical history.
(b)Seriousness of the disease.
(c)Tolerance of the child for specific medications, procedures and therapies.
(d)Expectation for the course of the disease.
(e)Opinion or preference from the side of the family about the treatment.
Treatment consists of daily doses of folic acid, blood transfusion, removal of spleen

Beta Thalassemia

Beta thalassemia is caused by the mutation in beta globin chains. Chromosome number 11 controls the beta protein. Two genes are needed to make beta globin protein chain. If one or both genes are mutated, the person will have beta thalassemia. If both are mutated, the condition is either beta thalassemia intermedia or beta thalassemia major. Intermedia cause moderate anemia and the major cause the severe anemia.
Beta thalassemia minor or carrier or trait: The person will be a carrier when one mutated gene is inherited and do not show any symptoms.
Beta thalassemia intermedia: This is a condition between carrier and major. These patients have hemoglobin of 7-9g/dl. The patients need blood transfusion, when their hemoglobin drops due to infection and stress on the body especially during pregnancy and leg ulcer.
Beta thalassemia major: In this condition children are normal at the time of birth but develop anemia during the first year of life. Growth failure, deformities, enlarged spleen and liver are some of the problems. This condition requires intensive medical care which includes 2-3 weekly transfusions, desferrioxamine injections for 8-12 hours at home. Transfusions can decrease the disease but the iron content increase due to transfusion may cause damage to heart, liver and endocrine systems. Associated diseases are diabetes, growth and puberty failure, early menopause and transfusion complications such as Hepatitis C, B and HIV.
For determining this disease simple blood test called hemoglobin Electrophoresis or hemoglobin A2 to understand, if it a carrier or not.
During pregnancy there are three ways to test the fetus:
(a)CVS- during 8-10 months of pregnancy.
(b)Amniocentesis- during 14-18 weeks of pregnancy.
(c)Fetal blood testing- Blood is taken from the umbilical cord of the fetus during 18-20 weeks of pregnancy.
First and third tests have a reported miscarriage rate of one out of 100 tests and second test one in 200.