What is a Karyotype and Why is It Important?

A karyotype is a form of chromosome testing that provides a snapshot of your complete set of chromosomes, the structures in a cell nucleus that contain DNA.

Geneticists often use it to detect irregularities in the structure or amount of your chromosomes (missing or excessive chromosomes).

Karyotyping can be valuable for diagnosing a suspected genetic disorder or assessing its inheritance risk. Let’s discuss the process further.

What is Karyotyping?

Karyotyping is the process of isolating your pairs of chromosomes from a cell and then arranging them in numerical order from largest to smallest.

It’s usually done when your chromosomes are in the metaphase stage, where your chromosomes are visible and easy to observe. After taking a sample of cells, a professional can observe your chromosomes.

Why Do Some Choose Karyotype Testing Over Other Test Methods?

Compared to some other genetic testing methods, karyotype testing is a more affordable and practical option.  While other tests can dive deeper into specific chromosomes, karyotyping can show you an overall review of your chromosomes. 

However, more specific tests may be ordered to look into certain details and confirm anything a karyotype test picks up.

Karyotype testing is also better at determining balanced rearrangements, which are structural variations or aberrations in chromosomes. These are often linked to infertility, something that other genetic tests can miss.

What are the Benefits of Karyotyping?

Karyotyping is most useful for detecting chromosomal abnormalities. It can help diagnose Down syndrome, some birth defects, certain cancers, and other genetic conditions that may affect your baby at the chromosomal level.

Aside from identifying genetic disorders and abnormalities, karyotyping can also determine the specific genetic factors that may cause them.

Karyotyping does this by looking for problems with chromosome structure or number, which often cause these illnesses. It can check if an unborn child has extra or missing chromosomes.

Abnormal chromosome count and anatomy can lead to health, growth, and development problems. It can also assess if your child’s chromosomes have structural abnormalities that can lead to a wide range of developmental delays.

What are the Limitations of Karyotyping?

Despite being a valuable tool for detecting genetic disorders, karyotyping is limited by its inability to accurately detect:

• Small-scale chromosomal changes
• Certain genetic conditions and hereditary diseases, like cystic fibrosis, Tay-Sachs disease, sickle cell disease, and dwarfism
• Complex aberrations or chromosomal changes that involve at least two chromosomes
• Marker chromosomes or extra chromosomes that don’t belong in any of the 23 pairs

What Can Karyotyping Detect?

Some of the most common chromosomal abnormalities a karyotype can detect include:

• Down Syndrome (Trisomy 21) – Caused by an excess chromosome 21, affecting a person’s physical features, cognitive functions, and behavior.
• Edwards’ Syndrome (Trisomy 18) – Occurs when there's an extra chromosome 18. Most babies born with Edwards’ syndrome have a low chance of surviving after birth because of health problems like heart defects, low birth weight, and respiratory problems.
• Patau Syndrome (Trisomy 18) – Results from an extra copy of chromosome 13. Most babies born with Patau syndrome don’t live more than a year because of heart problems and severe mental impairment.
• Klinefelter Syndrome – This happens when a boy baby has an extra X chromosome (XXY), which may slow puberty or affect their ability to reproduce.
• Turner Syndrome and Mosaic Turner Syndrome – Occurs when a baby girl has a missing or impaired X chromosome, resulting in problems with the heart, neck, and height.

How is a Karyotype Determined?

The process of determining a karyotype involves key steps such as:

• Sample collection — Karyotyping starts with a sample of your cells containing your chromosomes. 
• Cell culture — Geneticists will place the collected cells in the lab to have them cultured by placing them in an environment with sufficient nutrients.
• Arresting cell division — Geneticists will apply a chemical called colchicine to the cells to interrupt the cell cycle at the metaphase stage. This makes the chromosomes easier to count and observe.
• Staining — A special dye is used to bind with the DNA to produce branding patterns for different chromosomes. This helps mark the location of genes in a chromosome.
• Karyotype construction — Viewing stained cells under a high-powered microscope and capturing images of the chromosomes. They’ll then arrange these images according to size and shape.

What Are The Methods Of Collecting Samples For A Karyotype?

Karyotyping uses chromosomes from mitotic cells or cells capable of dividing. Only cells that can be induced to divide in a lab are used for karyotyping, such as:

• Peripheral blood lymphocytes — A type of white blood cell
• Skin fibroblasts — Main cells found in your skin connective tissue
• Amniocytes — Cells found in the amniotic fluid around a developing fetus

Geneticists often draw blood for karyotyping, but amniotic cell sample retrieval is also a possibility when pregnant. This involves a medical specialist inserting a long, thin needle into your abdomen to draw out the amniotic fluid.

However, cells from the bone marrow and chorionic villus can also be used since they divide quickly. Bone marrow is often used to determine certain blood diseases or cancers.

What is Chorionic Villus Sampling?

Chorionic Villus Sampling (CVS) is a procedure for obtaining cells from the chorionic villi tissues. Because the chorionic villi tissues are part of the placenta, they usually share the same chromosomes as the unborn fetus.

Geneticists can perform a CVS 10 to 13 weeks into the pregnancy, guided by an ultrasound scan. This helps prevent foreign materials from entering the sac.

CVS is usually done for higher-risk pregnancies, like pregnant women over the age of 35 or pregnancies with delicate circumstances. 

What Are the Risks of Karyotyping?

Taking a blood sample is relatively safe. However, there can be a risk of infection or bleeding around the collection site. 

Fortunately, most complications from blood sample karyotype collection are minor. On the other hand, there are some risks with the other methods that you should be aware of.

For example:

Amniotic Fluid Karyotyping Risks	Chorionic Villus Karyotyping Risks
Bleeding or leaking from the collection site	Miscarriage (extremely rare)
Some cramping or abdominal discomfort	Limb deficiencies if the test is done before 10 weeks
Infection (rare)	Abdominal discomfort and cramps
Preterm labor (rare)	Infection
Injury to the fetus from the needle touching them accidentally	Rupture in the amniotic sac

Keep in mind the risks associated with amniotic fluid karyotyping are increased if you get tested before the fetus has reached 15 weeks.

What to Consider Before Deciding on Karyotyping

Here are some things to consider:

• The cost of genetic testing and insurance coverage
• Genetic counseling
• Risks and complications, like bleeding, infection, or even pregnancy complications
• Emotional responses to any discoveries that karyotyping may show

What to Do After Karyotyping

After doing proper aftercare following your procedure, follow your doctor’s orders. If they tell you to get bed rest or that you can’t drive right away, make sure you listen. Wait for your results patiently and ready yourself for any potentially distressing news. 

Your doctor may encourage you to seek some professional help from a geneticist, genetic counselor, or psychology expert to help you understand any results you weren’t expecting.

Once you have the results, don’t jump to conclusions without consulting an expert to interpret them. Being at an increased risk for congenital disorders does not guarantee development. 

Find out what you can do to make your life or your baby’s life as easy and complication-free as possible.