Cytogenetics can determine any abnormalities or structural problems within the chromosomes of an organism by examining them through the process of karyotyping. As medical genetics is becoming an important field of study, it is increasingly integrated with clinical medicine to analyze and treat physical and mental illnesses in humans.
What Is Karyotyping?
Normal Karyotyping, commonly known as genetic, chromosome testing, or cytogenetic analysis, is a laboratory procedure to create a photographic image of an individual’s chromosomes. This test is done to rule out the possibility of genetic disorders in the unborn child due to Chromosomal abnormalities, including numerical and structural changes of a baby’s chromosomes. Chromosomes are found in the nucleus of every cell of a living organism. These thread-like structures largely determine or make us who we are, determining our physiological and psychological development and function. A human cell contains 46 chromosomes. If the count of chromosomes is other than 46, it suggests an association with aneuploidy conditions linked to developmental issues. A study of karyotypes that seeks to identify the specific reasons for the chromosomal count variations such as deletions, additions or translocations, etc., can identify the type and severity of the problem. However, even with the same chromosome abnormality, it is also possible that two individuals may experience a different level of difficulty. Apart from this, Karyotypes are also used to study taxonomic relationships, cell function and understand human evolution.
Why Is This Test Important?
The test examines the chromosomes to confirm if the chromosome count adds up to 46 and if each of the 46 chromosomes is normal in its structure and appearance. A chromosome extra or less could mean excess or shortage of genetic building blocks needed for a normally functioning human body, leading to different types of complications. The size and significance of the problems depend on the chromosome or part of the chromosome that is changed, missing, or excess. During pregnancy, a much different prenatal screening is advised. Several types of genetic disorders can be diagnosed using karyotyping. This test is offered during the first and second trimesters to most pregnant women. The follow-up tests are done to determine the severity and exact nature of the problem. Karyotyping tests for miscarriages or infertility help doctors determine if the cause relates to a chromosome abnormality. Karyotyping also helps determine if any parents have a hereditary disorder in nature and can be passed down to the baby. You can even test a stillborn baby to check for underlying genetic issues. Abnormal chromosomes refer to both structural as well as numerical changes. Karyotyping of down syndrome or Karyotyping of turner syndrome are examples where the tests can identify several developmental and growth, and function-related issues early. Most parents opt for karyotyping tests to ensure that the child coming to the world is healthy and has a life full of potentials ahead of him/her. Though complicated, these tests are now the gold standard in screening, confirming, and avoiding future suffering for both parents and children.
Types of Karyotype Tests
Late parenthood generally increases the likelihood of a chromosome-related problem, for example, those 35 years and older. Other risk factors are genome-related. The risks are higher if you already have a child or a hereditary or family history of a chromosome disorder. Also, if you or your partner has an unusual chromosome, or if you have had miscarriages or stillborn babies in the past. Karyotype tests are feasible only during a specific period of your pregnancy. Your obstetrician would suggest the timing and type of karyotype test should be done based on the trimester of pregnancy you are in and on your medical history. These delicate and susceptible procedures require technical expertise and experience to carry out and explain the results effectively. Among the Karyotype tests, the following are the most common:
1. Chorionic villus sampling -CVS
A tiny sample of the baby’s cells is collected from the placenta using a long needle. These cells are then sent to a laboratory for testing. The testing results confirm the existence of a genetic problem, including Down Syndrome for your baby. CVS can be done between ten and thirteen weeks of pregnancy. Your doctor would advise you about the risk factors associated with the test. There is a 1% chance of miscarriage in women and some risk to the baby as well. Therefore, the test is advised by doctors in cases where there is a high probability that your baby has a problem.
In theory, any cell from the body can be used to perform chromosome testing. However, in reality, the test is usually carried out on the amniotic fluid of a fetus. In this test, doctors insert a needle through the abdomen to collect a small amount of “amniotic fluid” from your womb. Afterward, the cells are sent to a lab for testing. The lab test results lead to determining your baby’s future health and link to genetic problems. This test identifies neural tube defects in addition to the defect that the CVS testing can find. Neural tube defects are severe problems that affect the baby’s brain or spine. Amniocentesis is normally performed between the 15th and 20th weeks of pregnancy. With a 0.05% probability of a miscarriage, this test provides a significantly better risk profile than CVS.
Procedure for the Test
Although it may sound like a simple blood test, a karyotype test actually involves quite a complex procedure. Karyotypes are performed in a specific laboratory called a cytogenetics lab which specializes in karyotype analysis. Let’s take a look at the steps involved:
- To examine chromosomes, the lab needs cells that are actively dividing, like the fetal cells in the “amniotic fluid” and “chorionic villi” of a pregnant woman. The sample is collected using the Amniocentesis or chorionic villus technique.
- The sample is then processed using chemicals for cell culture to collect the dividing cells. This process can take up to seven days.
- The next step is to count the chromosomes under a microscope. This is possible only during the metaphase of cell division when the chromosomes are most compact. This is achieved by treating the cell culture with specific chemicals, which stops the cell division at the required stage.
- Chromosomes are colorless. So a special dye is used to differentiate one chromosome from another. Once the dye is applied, the chromosomes start to look like intertwined strings of light and dark bands with specific patterns.
- Microphotographs are taken of the chromosomes.
- And just like a jigsaw puzzle, the microphotographs of the chromosomes are arranged to match up the pairs by size.
- It is now that the counting starts. Most of us have forty-six chromosomes. In Down syndrome or other such conditions, the individual may have extra or fewer chromosomes or maybe have portions of a chromosome missing or duplicated or translocated or interchanged.
- The number of chromosomes tells the cytogeneticist whether the sample is normal or special with a link to a specific condition.
Karyotype analysis requires experience and expertise to perform properly and to interpret the results.
- The primary risk associated with the procedure used to gather cells for karyotype testing is miscarriage.
- Another risk associated with the procedure is that of secondary infections and resulting harm to the fetus.
Results of Karyotype Tests
After karyotype testing, the lab usually sends the results after two to three weeks of checking your baby’s chromosomes. It gives information on any specific genetic mutations that are present such as that cause cystic fibrosis. You may repeat the karyotype test to confirm that there’s an abnormality. However, these tests lead to a more definitive answer than screening tests used earlier. Earlier tests used to provide the high or low chances of a problem in the past. So, if your baby has a genetic problem, your genetic counselor would help you understand what can be done and what cannot. Further studies may also be needed to evaluate the possible role of gene mutations in disease or miscarriages.
Molecular cytogenetics is a dynamic discipline, and new diagnostic methods continue to be developed. The cost of genetic Karyotype testing can range from under $100 to more than $2,000, depending on the nature and complexity of the test. In contrast, karyotype test costs, on average, US $11,033 per diagnosis. Though you may feel anxious or devastated to know about genetic abnormalities in a fetus after Karyotype testing, learning about some of the conditions associated with them may be helpful. In fact, many people who are living in these conditions enjoy an excellent quality of life.