What is a Karyotype and Why is It Important?

Key Takeaways

• Karyotypes are images of chromosomes, helpful in diagnosing genetic disorders - Jump to Section
• Karyotyping detects genetic diseases by analyzing chromosome structure and number - Jump to Section
• Karyotyping involves cell collection, culture, staining, and arranging chromosomes - Jump to Section
• Samples for karyotyping are collected via blood tests, amniotic fluid, or CVS - Jump to Section
• Karyotyping can detect abnormalities like Down syndrome and Klinefelter syndrome - Jump to Section
• Karyotyping can miss small chromosomal changes and complex genetic conditions - Jump to Section

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.¹

Geneticists may use it to detect irregularities in either structure or your chromosome count (missing or excessive chromosomes).

Karyotyping is the process of isolating your pairs of chromosomes from a cell and then arranging them in numerical order from largest to smallest.²

Karyotyping can be valuable for diagnosing a suspected genetic disorder or assessing its inheritance risk. This is usually done for pregnant women, determining causes of infertility, cancer diagnosis, or just determining risk for any genetic disorder.

What is a Karyotype?

A karyotype is a lab-produced image of your complete set of chromosomes.

Karyotyping is usually done when your chromosomes are in the metaphase stage. After taking a sample of cells, a professional can observe your chromosomes.

Metaphase is the third phase of the cell division process. During metaphase, your chromosomes are lined up in the middle of the cell. They are most visible and well-defined this way, so it’s easy to count, observe, and identify them.

Karyotyping can be most useful for detecting chromosomal abnormalities. It can help diagnose genetic disorders like Down syndrome, some birth defects, and even certain cancers.

Why is Karyotyping Important?

Karyotyping can help detect genetic disorders and abnormalities related to your chromosomes, since they are genetic material. It is an important way to determine if you (or your fetus, if you’re pregnant) have a genetic disease.

If, for example, you’re struggling to get pregnant, structural abnormalities revealed by a karyotype test may determine what genetic factors may be causing it. Conversely, you may already be pregnant and want to get a quick idea of what genetic conditions may affect your baby at a chromosomal level.

Image from National Human Genome Research Institute

Karyotyping does this by looking for problems with chromosome structure or number, which often cause these illnesses.

A karyotype can check if an unborn child has extra or missing chromosomes in prenatal testing. It can also assess if any of the chromosomes have structural abnormalities, which can lead to a wide range of developmental delays.

There are 46 human chromosomes in each cell, which come in pairs. The first 22 pairs are called autosomes. The 23rd pair is the sex chromosomes. Males and females have different sex chromosomes. Men have one X and one Y chromosome, while women have two X chromosomes.

Abnormal chromosome count and anatomy can lead to health, growth, and development problems.

Why Do Some People Choose Karyotype Testing Over Other Test Methods?

Compared to some other genetic testing methods, karyotype testing is a more affordable, practical option.

While other tests can dive deeper into specific chromosomes, karyotyping can show you a good overview of all your chromosomes to determine any abnormalities. Usually, more specific tests are ordered to look into certain chromosomes and to confirm anything a karyotype test picks up on.

Karyotype tesing is also better at determining balanced rearrangements, which are structural variations or aberrations in chromosomes often linked to infertility. Other genetic tests can miss this.

How is a Karyotype Determined?

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

Sample Collection

The process of karyotyping starts with obtaining a sample of your cells containing your chromosomes. Geneticists often use blood draws, but amniotic cell sample retrieval is also a possibility when pregnant.

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:³

• 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

However, cells from the bone marrow and chorionic villus can also be used since they divide quickly.³

When determining certain blood diseases or cancers, a bone marrow test may be used to harvest cells for karyotype.

Cell Culture

Geneticists will place the collected cells in the lab to have them cultured. They’ll be put in an environment with sufficient nutrients to stimulate them to divide.

Arresting Cell Division

Geneticists will apply a chemical called colchicine, a plant alkaloid extracted from the autumn crocus flower, to the cells to interrupt the cell cycle at the metaphase stage.

It prevents the formation of the mitotic spindle fibers necessary for cell division. The cells become stuck in metaphase as a result.

In karyotyping, it’s easier to count and determine abnormalities of metaphase chromosomes. It’s because they are condensed and tightly coiled, which makes them easier to see and count.

Chromosomes are more dispersed and less easily distinguished from one another in later phases of the cell cycle.

Staining

Geneticists will place the cells on a slide and stain them with a special dye. Giemsa stain, a visible light dye, is the most commonly used for karyotyping.

The dye binds with DNA and produces banding patterns for different chromosomes. A banding pattern is made up of the alternating light and dark regions in a chromosome.

It marks the location of genes in a chromosome.

Karyotype Construction

Geneticists will view the stained cells under a high-powered microscope and capture images of the chromosomes. They’ll arrange the images of these pairs of chromosomes according to size and shape.

What Are The Methods Of Collecting Samples For A Karyotype?

Here are the different ways to collect samples for karyotyping.

Blood Sample Karyotyping

A blood test is often the simplest way to obtain cells for karyotyping. Blood samples have peripheral blood lymphocytes, which can be used for a karyotype.

A specialist will draw your blood sample from a vein in your arms. They will then send your specimen to a lab to be cultured and stimulated to divide.

Once the chromosomes enter metaphase, the geneticists will stain and photograph them for chromosome analysis.

Risks of Blood Sample Karyotyping

Taking blood samples is relatively safe and a routine procedure for plenty of healthcare facilities, labs, and hospitals. However, the most common risks are infection or bleeding at the collection site.

Most complications from blood sample karyotype collection are pretty minor, but be sure to follow your healthcare provider’s instructions when you get your blood taken.

Amniotic Fluid Karyotyping

Amniotic fluid karyotyping is performed with the steady guidance of ultrasound images when you’re pregnant. The medical specialist inserts a long thin needle into your abdomen and draws out amniotic fluid.

The amniotic fluid contains fetal skin cells shed by the fetus. Geneticists can retrieve the skin cells by extracting the fluid using a syringe.⁴

The needle goes through the amniotic sac and collects a small fluid sample for analysis.

Amniotic fluid karyotyping is generally a safe procedure. Still, to exercise caution, geneticists typically perform it between 15 and 20 weeks of pregnancy to minimize the risk of complications, such as miscarriage.⁵

Risks of Amniotic Fluid Karyotyping

Most amniotic fluid collection procedures come with some potential risks, as well, such as:

• Bleeding or leaking from the collection site
• Some cramping or abdominal discomfort
• Infection, though this is rare
• Preterm labor, although this is also rare
• Injury to the fetus (the needle may accidentally touch them)

These risks are increased if you carry the testing out before the fetus has reached 15 weeks.

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 do a CVS ten to 13 weeks into the pregnancy. They perform it while being steadily guided by an ultrasound scan. This helps prevent foreign materials from entering the sac.⁶

Risks of Chorionic Villus Karyotyping

CVS is usually done for higher risk pregnancies, like pregnant women over the age of 35 or pregnancies with delicate circumstances. That being said, there are a few more pronounced risks, such as:

• Miscarriage (although this is about a one in 100 chance)
• Limb deficiencies (especially if done before ten weeks)
• Abdominal discomfort and cramps
• Infection
• Rupture in amniotic sac

What are Some Common Chromosomal Abnormalities?

It’s easy to see how significant karyotyping is in finding chromosomal problems, given how crucial it is to have the right number and shape of chromosomes.

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

• Down Syndrome (Trisomy 21) — Occurs when there’s an excess or a third copy of chromosome 21. It affects a person’s physical features, cognitive functions, and behavior.⁷ For instance, people with Down Syndrome are typically shorter than average.
• Edwards’ Syndrome (Trisomy 18) — Happens when there’s an extra or a third copy of chromosome 18. Most babies born with Edwards’ syndrome have low chances of surviving after birth since they are usually born with many health problems like heart defects, low birth weight, and respiratory problems.⁸
• 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 — 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.

What are the Limitations of Karyotyping?

Despite being a valuable tool for detecting genetic disorders, karyotyping has some limitations. Karyotyping is limited by its inability to accurately detect:⁹

• Small-scale chromosomal changes
• Certain genetic conditions and diseases that run in families, like cystic fibrosis, Tay-Sachs disease, sickle cell disease, and dwarfism¹⁰
• 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 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 from a psychology expert in case you need to unpack any results you weren’t expecting.

Don’t jump to conclusions based on your results, especially without an expert to interpret your results with you. A 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.

Common Questions About Karyotypes