Karyotyping test – Purpose and Procedure

What is karyotyping?

Karyotyping is the process of pairing all the chromosomes of an organism, which provides a snapshot of the genome of an individual. A genome is a complete set of DNA or genetic material in an organism. The genome contains the information that is needed for an organism to grow and develop.

The procedure is prepared using a standardised staining procedure, which reveals the characteristic structural features of each chromosome.

With the help of clinical cytogeneticists, they will be able to analyse human karyotypes and detect any genetic changes like anomalies. They also reveal the changes in the chromosomal number like deletions, duplications, inversion and translocations. According to research, karyotyping is a source for diagnosis and detects congenital disabilities, cancers and genetic disorders.

The chromosomes are present in every cell, and when the cell divides, the information in the previous cell should be transferred to the new cells. When cell division does not occur, the chromosomes get arranged in an unorganised way.

The karyotype test analyses the dividing cells by the arrangement of their size and appearance. The test will help the doctor to diagnose if any chromosome is damaged or misplaced.

When is karyotyping needed?

If a couple is planning for pregnancy or a woman is pregnant, karyotyping will be required. When the maternal and the paternal have a defective gene, it can pass to the baby, karyotyping helps determine defective genes.

It can also analyse a woman’s possibility of getting pregnant and the reasons for miscarriages.

Check for the genetic disorders of the unborn child and any other risks. Genetic or birth defects can be high.  

A karyotype test will also be required for the following reasons.

• If a pregnant parent is 35 and above
• If a maternal or paternal has a genetic disorder or a family history of the genetic disorder.
• The results of the parental screening are not normal.
• A karyotype can be used to diagnose the risk factor for developing a chromosomal disorder.
• When a mother and child both have a genetic disorder, the symptoms can be different for the same disorder. In such cases, the karyotype is recommended.
• When a person is affected with a certain type of blood disorder or cancer, that alters the chromosomes. The treatment will depend on these changes and will require a prompt diagnosis for effective treatment.
• Some of the common conditions that can be diagnosed and treated effectively with the help of karyotype tests are
• Leukaemia
• Multiple myeloma
• Anaemia
• Lymphoma.

Who performs a karyotype test?

A karyotype will be performed by a professional. The blood will be drawn by a lab technician, and it is stored until the blood is analysed by a pathologist or a geneticist.

Types of karyotype tests

Karyotype tests can be done in different forms.

• Blood test
• Bone aspiration  
• Biopsy
• Amniocentesis
• Chorionic villus sampling (CVS)

The blood test is the most common type of karyotyping test. The blood test can be done for infants, adults and children. The blood will be collected by a professional and will be analysed in a laboratory, and the results will be shared with your doctor.

Bone aspiration is a test where the sample of bone marrow is removed for diagnosis purposes. The biopsy is the same technique as the bone aspiration.

The bone aspiration will be performed by a professional who specialises in the fields of oncology and haematology. The test will be done in a clinic.

The following procedure will be carried out during the test.

• A sedation will be suggested for people who are undergoing the test to relax.
• The person subjected to the diagnosis will be made to lie on their side or stomach.
• For people without any sedation, local anaesthesia will be given near the top of the hip bone so the person will feel less pain or no pain.
• The professional will then insert a thin needle through the bone, and a sample of bone marrow fluid will be collected.
• For the biopsy test, a sample of solid bone marrow tissue will be collected.
• During the procedure, the person may feel some amount of pain or pressure.

The amniocentesis test requires a sample of amniotic fluid. The amniotic fluid is a fluid that surrounds the developing foetus and acts as protection for the child. The collected fluid will be analysed in the laboratory, and the results will be given. Amniocentesis is usually done between the 15th and 20th week of the pregnancy.

The procedure will occur as listed below.

• The pregnant woman will lie on their back, and the professional will perform an ultrasound. The technique will help to check the foetus and the uterus of the woman for any abnormality.
• The ultrasound will also help to guide a thin needle through the belly and then to the uterus. Additional care will be taken not to harm the foetus.  
• The needle then passes through a thin membrane around the foetus that contains the amniotic fluid called the amniotic sac.
• Local anaesthesia or a numbing medication will be given before inserting the needle to reduce pain. However, the person will feel some amount of pain, like cramping or stinging, during the procedure.

The chorionic villus sampling (CVS) procedure collects tissues from the chorionic villi. The chorionic villi are a part of the placenta with the same chromosomes as the foetus. The chorionic villus sampling will be done during the 10th and 13th weeks of pregnancy.

The test is similar to that of amniocentesis. The procedure occurs as listed below.

• The pregnant woman will be made to lie on their back, and an ultrasound will be performed, which helps to see the foetus and the uterus.
• A catheter will be inserted through the cervix or a needle through the belly with the help of ultrasound. The catheter or the needle will reach for the placenta.
• The needle or the catheter will collect a sample of cells from the placenta.

Why is the test required?

A karyotyping test will check for the set of chromosomes. If there is an increase or decrease in the chromosomal number, it can indicate a health condition like Down syndrome or Turner syndrome.

The test will also check for any damaged, misplaced, substituted and deleted chromosomes. These changes can cause minor to major health issues. In some cases, certain changes in chromosomes will not cause any problems.

However, certain chromosomal problems can occur during birth or develop after birth. So, karyotyping will help to identify these health conditions or diseases. The test can also identify infertility, the reason for miscarriage and also helps plan treatments effectively.

Preparation for the test

The preparation for the test will depend on the type of the test. For a blood test, preparation will not be required. However, the person will be asked to drink enough water for CVS or amniocentesis until their bladder is full. This will help with the ultrasound process.

What do the test results mean?

The test results may take up to a few weeks or even a lesser time. Consult the professional about when you can expect the test results. A normal result of the karyotyping will indicate that the person has 46 normal chromosomes without any abnormality or unusual change.

Abnormal test results could indicate that a person or the foetus has a disorder related to chromosomes. Abnormal test results can indicate the following genetic diseases or disorders that are listed below.

• Down’s syndrome can cause delayed growth and affects intellectual abilities.
• Edward syndrome can cause health issues related to the kidney, lungs and heart.
• Patau syndrome leads to low birth weight and poor development of the uterus.
• Turner syndrome prevents or delays the development of secondary sexual characteristics in women.

Conclusion

Karyotyping is a diagnostic technique that helps identify abnormal changes in chromosomes. They are usually recommended to diagnose certain types of cancer and blood disorders.

The test will also help to detect the risk factor for a certain types of genetic disorders. The karyotype test will be suggested by a healthcare professional. Consult your geneticist before taking the test. They will help you with the benefits and risks of the diagnostic procedure.

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