The Thalassaemia

The Tests

1. There are 3 tests available. Although each test has its respective merits and has to be done at its own optimum time, CVS is the most commonly offered test. These tests are different from the blood test, the hemoglobin electrophoresis, used to determine a Carrier. There are three tests available. The Chronic Villas Sampling (CVS) Test is done from 10 weeks of pregnancy, Fetal blood sampling from 18 weeks and the rarely done Amniocentesis is between 14-18 weeks. 

2. The choice of which test to use is a very carefully considered matter. However, if the mother has presented herself early in a pregnancy, Chronic Villas Sampling is the best test because of the ease of doing it and its acceptability to the mother as it can be done earlier in the pregnancy. 

3. Chronic Villas Sampling (CVS) test involves taking a small sample of the developing placenta from 10 weeks of pregnancy. The placenta, which is attached to the growing fetus by the umbilical cord, contains the DNA imprint of the baby. The placenta and its position is first assessed by ultra sound. A sample of the placenta is obtained either through the vagina or through the abdomen dependent upon where the placenta is located. The sample of placenta has its DNA then tested to see if the child's Hemoglobin making genes are affected and this determines if the baby has the full blown condition Thalassaemia Major. 

4. Fetal blood sampling involves test the taking of a blood sample from the umbilical cord of the fetus in the womb. Fetal blood sampling is used when the fetus has developed more and the pregnancy has advanced to 18-22 weeks. An affected baby will have little or no adult Hemoglobin HbA. This test is used when the CVS test cannot get access to the placenta or when the DNA test cannot determine the exact DNA profile of the baby. 

5. Amniocentesis involves taking a small sample of the amniotic fluid that surrounds the baby. As there are very few cells from the baby floating about in the amniotic fluid, the test requires culturing and growing of the captured cells in the laboratory and then the DNA of these cells is tested as per the placenta test. 

6. EASE OF SAMPLING AND TESTING: The CVS has merits as you can take a sample from a sizeable placenta and have a DNA test made available within 5- 10 days. Fetal blood sampling requires getting access to the small umbilical cord and then measuring the Hb A or DNA- it can be difficult. Amniocentesis requires a cumbersome process as it requires looking for Fetal cells in the amniotic fluid and then the culturing of the cells in addition to the DNA test. 

7. PSYCHOLOGICAL ASPECTS OF TESTING: It is reported that the earlier a test is done in a pregnancy, the lesser the psychological factors affecting the mother and couple. CVS is done from 10 weeks and is very early in the pregnancy and the mother has not developed a deep bond with the pregnancy- especially when it is not showing and/ or has not been physically demanding. Fetal blood sampling is quite late and will be more demanding psychologically where termination of a pregnancy is a considered option. 

8. SAFETY AND ACCURACY: CVS and Fetal blood sampling has a reported miscarriage rate of 1 in 100 (1%) tests. Amniocentesis has a 1 in 200 miscarriage rate. 

9. ETHICS OF TESTING: The following comments from Professor Marcus Pembrey in the Progress Guide to Genetics (Progress Educational Trust) are appropriate to bear in mind: “The technical aspects of the testing process are getting simpler year by year, but this does not mean the decisions that people have to make are easier. Testing must be linked to adequate counseling, exploring what they would feel and how they would cope if they tested positive” 

Thalassaemia And The Public Health 
The Impact Upon The State, Community And The Individual 

Genetic disorders like Thalassaemia Major will become a major policy issue during the next century. Genetic disorders will begin to have a disproportionate impact upon the State when their treatment and management is compared to that of the traditional illness and epidemics. Preventative education and vaccination has removed the spectre of many illness from our communities. Advances in sanitation and Public health infrastructure have reduced the incidence of the major killers that plagued our ancestors. 

Genetic disorders have no cures. Treatments for genetic disorders are life long, involve painful protocols, absorb expensive and rare drugs, require constant monitoring and control, need disproportionate time from the consultants, rotate around the near full-time involvement of the nurses, counselors and other socio-psychological professionals. 

The impact upon the State's health, social welfare, education and overall economic system is enormous. It takes £1 million to raise a Thalassaemia Major child to Adulthood (30 yrs). The impact upon the individual and his/her family is immeasurable. The physical effects of the condition, the side effects of the treatment and the caprice of sexual development and growth can place an enormous psychological burden upon the individual. 

Glossary

Most of the terms and terminology of genetics can be found in good Genetic text books and dictionaries. We provide a few useful terms that relate to Thalassaemia in this section 

Autosome/ Autosomal genes: These are genes located on chromosomes other than the gender pair chromosome number 23. The conditions linked with autosomal genes affect both genders equally. Boys as 
well as girls are affected. In b (beta) Thalassaemia the mutation occurs on a pair of b goblin genes on chromosome 11. 

Dominant genes: The genes function differently to the recessive genes. In order for you to develop the full condition you need only one gene. The individual who carries this gene develops the full condition. Some common Dominant gene caused conditions are Huntington’s neurological disorder and Adult polycentric kidney disease. 

Hemoglobin electrophoresis test: This a test that takes a sample of your blood and tests your hemoglobin types. It is a very reliable way of determining if you are a carrier. This is not a DNA test. 

Genes: Genes are the building blocks of life. They are responsible for making all the proteins that the body needs to build muscles, bones, hormones and blood. We inherit our genetic blue print on approximately 100,000 pairs of genes. The DNA of the genes holds the code for all the human body. The 2 pairs (4 in number) of a(alpha) genes on chromosome 16 and 2 b (beta) genes on chromosome 11 are responsible for making the proteins needed for hemoglobin in the red blood cell. 

Mandolin inheritance: Named after Gregor Mendel a Swiss Monk who discovered that in pea plants some genes are dominant and some recessive. In recessive genes he discovered that in order for them to express themselves they need two copies one from each parent. In dominant genes you need only one. He, however, discovered another important fact that if both parent plants were carrying a particular recessive gene, then there was a probability that 50% of the offspring plants would carry the gene like the parents, 25% of offspring plants will not inherit that gene and 25% offspring plants will inherit both the genes and the gene will then express itself: e.g. red flowers in offspring from two pink flowered parents. This inheritance pattern has a big implication on testing, screening and prevention when managing public health programmes in recessive gene disorders. 

Recessive genes : Recessive genes work in pairs. This means that in order for someone to develop a recessive gene related genetic condition. That individual must inherit two faulty genes: One from each parent. Mandolin inheritance patterns of inheritance occur. There is a 25% chance at each pregnancy that the child will have the full blown condition. A Thalassaemia Carrier has one Thalassaemia Gene and so does not suffer the full blown condition. 

Tests for carriers: Genetic science has given us the ability to test an individual for many conditions. In Thalassaemia we do not need a DNA test to identify the Carrier. We use the Hemoglobin electrophoresis test that takes a sample of your blood and tests your hemoglobin types. It is a very reliable way of determining if you are a carrier. In other genetic disorders we must use a DNA test. A small sample of the individuals tissue or body sample is taken and a DNA test applied. The individual will reveal mutations on the genes we are looking for. 

Tests for pregnancies: These are DNA tests that are performed on tissue samples taken from the fetus or on foetal cells floating in the amniotic fluid. In Thalassaemia the chronic villous sampling test involves taking samples of the placenta, the big tissue that attaches the baby to the mothers womb, and then doing DNA tests on it. This is a reliable test and can be done as early as 10-12 weeks of pregnancy.

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