Karyotyping - Advantages and Disadvantages

Introduction:

Karyotyping is the method to analyze chromosomal abnormalities in terms of chromosomal structural abnormality or numerical abnormality. The karyotyping technique focuses on localizing and visualizing a particular genetic component on a chromosome. With the help of this technique, a chromosomal profile of an individual can be made, which helps in studying the individual's genetic makeup. The karyotyping technique aids in the early diagnosis of any genetic disorder by relocating the causative gene (inherited condition due to DNA or deoxyribonucleic acid abnormality).

What Is the Role of Karyotyping in Medical Genetics?

Karyotyping is the most preferred method for the cytogenetic study. The following are the indications for karyotyping:

1. Analysis of Cancerous Conditions:

• For diagnosing and classifying leukemia.

• Depicting the prognosis of cancer.

• Evaluating the treatment plan.

• Checking elimination of abnormal genotype (genetic constitution of an individual) post-treatment.

2. Analysis of Congenital Disorders:

• Ultrasound reports depict abnormality.

• Abnormal biochemical parameters.

• Miscarriages.

• Family history of genetic disorders.

What Is the Process of Karyotyping?

The following steps are followed in the process of karyotyping:

1. The first step begins with the individual's collection of mitotic cells (dividing cells). This genomic sample can be collected from almost any tissue, but the following sources are recommended-

• Amniotic fluid.

• Blood.

• Bone marrow is most preferred.

2. Staining the given cell sample is done. Giemsa stain is most commonly used for staining purposes for karyotyping.

3. After staining, the cell is observed under bright-field microscopes.

4. A photograph of the stained sample is captured to visualize the chromosome. This stained cell sample used for chromosomal analysis is called a karyotype, and the process is called karyotyping.

What Are the Normal and Critical Findings in Karyotyping?

It is known that every human cell is composed of 23 pairs of chromosomes, out of which 22 pairs are autosomes, and the other pair is a sex chromosome (XX for male, XY for female). Autosomal chromosomes are sorted by size. So, any chromosomal finding similar to the natural existing chromosomal number and structure is considered normal. Whereas, Critical findings include the following features:

1. Aneuploidies.

2. Missing chromosomes.

3. Structural abnormalities like:

• Translocation.

• Duplication.

• Deletion.

• Inversion.

• Insertion.

The general meaning of each critical finding with examples is as follows:

1. Aneuploidies: The presence of one or more extra chromosomes. Examples of aneuploidy as seen in genetic deformities like Down's syndrome (trisomy of 21st chromosome) and Klinefelter's Syndrome (presence of XXY chromosome).

2. Missing Chromosomes: It describes the condition where only one chromosome is present, and the other one is absent from the pair of chromosomes. In such cases, the individual has only 45 rather than 46 chromosomes. Turner syndrome (monosomy of X) is a genetic disorder showing a missing chromosome.

3. Structural abnormalities:

• Translocation: It describes the abnormal arrangement of chromosomes. In such cases, a part of one chromosome breaks off and gets attached to another chromosome. For example, as seen in the translocation of Down syndrome. An additional copy of chromosome 21 gets attached to another chromosome in this syndrome.

• Duplication: It describes the situation in which more than one copy of a DNA segment is produced. For example, in MECP2 duplication syndrome, each cell has an extra copy of the MECP2 gene.

• Deletion: It describes the genetic change where one of the DNA segments gets deleted, for example, Williams-Beuren syndrome.

• Inversion: It describes a condition where a part of a chromosome breaks off and is reattached in the reverse direction, for example, hemophilia.

• Insertion: It describes a condition in which one more nucleotide gets attached to a DNA fragment.

These critical findings are pivotal in diagnosing syndromes, congenital diseases, and various cancers.

What Are the Advantages of Karyotyping Procedure?

The following are the advantages of karyotyping tests:

• Even though a single karyotyping test is done, significant information can be obtained regarding the genetic build-up of the patient.

• It diagnoses primary as well as secondary anomalies (disorders).

• Karyotyping test results do not require reconfirmation through histological tests (examining a sample of tissues under a microscope).

• It is a very useful tool for diagnosing genetic disorders.

• The test results are precise, which helps in the definite diagnosis of the case.

• These tests are easy to carry and cause the slightest discomfort to the patients as the sample collection for the test is done using fine-bore needles.

• Karyotyping tests can detect genetic variations missed from procedures like polymerase chain reaction (PCR).

What Are the Limitations of Karyotyping Procedures?

The following factors are responsible for less awareness and practice of karyotyping:

• High Expenses: It is an expensive procedure; hence, many patients cannot afford it, so doctors refuse to carry out karyotyping tests for genetic study.

• Confirmation Bias: It is a commonly noted issue that misinterprets a karyotype. For example, the professional performing the process must be better aware of the various differential diagnoses of a particular genetic disorder. In that case, they will focus on a specific diagnosis resulting in inappropriate testing results. This condition could be stated as confirmation bias in karyotyping tests.

• Inappropriate Sample Collection: Karyotyping tests involve in vitro procedures. So, cell type selection is essential. Mitotic cells, which are in the metaphase stage of mitosis (a type of cell division in which two daughter cells are produced), are required for the karyotyping test. Failure to do so may result in inadequate testing.

Various research is currently going on to overcome these limitations of karyotyping. These modifications will contribute to uplifting medical genetics.

What Are the Patient Safety and Education Protocols Related to Karyotyping Tests?

• Every patient should know the probability of false positive results of such tests.

• Doctors must inform the patient about the sample collection procedures and associated risks.

• Clinicians should motivate patients to undergo these tests to diagnose the genetic disorder in their child or individual at the earliest.

• If the cytogenetic test shows positive results for the fetus, a pregnant lady; must be counseled about the probability of their child getting the genetic disorder and the associated fetal or maternal risks.

Conclusion:

Cytogenetic tests like karyotyping have broadened the horizon of medical genetics regarding diagnosis and planning treatment protocols for various genetic disorders. Multiple types of research are currently going on to overcome the limitations of genetic testing.