Have you ever heard of this 'FISH test' (Fluorescence in Situ Hybridization Test)? Perhaps your doctor has asked you or someone you know to do this test. Although it may sound a bit complicated, it is a very important test that can detect many things inside our bodies. So today, let's talk about what this FISH test is, what it does, and how it is done in a simple way that you can understand.
What is this FISH test (Fluorescence in Situ Hybridization)?
Simply put, FISH is a genetic test. Pathologists, who are doctors who specialize in diagnosing diseases , use this method to identify diseases caused by changes in the small things called chromosomes in our bodies. Sometimes, this test can also help identify genetic changes that can be treated for diseases like cancer.
Think of it this way: our genes are like an instruction book for our bodies. This instruction book tells us how everything in our bodies works. These genes are located in structures called chromosomes, which are like strings. So, what happens if some of the words in this instruction book, our DNA (deoxyribonucleic acid) , are deleted, or if there are too many words, or if some words are transposed? Our cells get the wrong instructions. In this way, information can be lost (deletion), copied more than necessary (amplification), or moved (translocation). These changes can change the way our bodies function and cause diseases like cancer.
So, what this FISH test does is, it's like using colored pens to "color" specific parts of chromosomes or genes. Then, those specialist doctors can easily find the parts they need to diagnose diseases by looking at them under a microscope. When you look at this color under a microscope, it looks like colored lights.
What can be detected by the FISH test?
Then you might be wondering, what exactly can be found with this FISH test? The main things are:
- Identify large-scale gene mutations in cancers. Using this information, doctors can accurately diagnose the type of cancer and choose the best treatment for it.
- Check for any chromosomal abnormalities before a baby is born (prenatal) or after birth. This helps to detect some genetic conditions early.
- In vitro fertilization (IVF) involves testing the embryo for chromosomal abnormalities before it is implanted in the mother's uterus (preimplantation genetic testing).
How does this FISH test work?
Okay, now let's see what the little secret is about how this FISH test works.
I've said before that our DNA is like a big instruction book. So this FISH test is like highlighting the most important parts of that instruction book with a special fluorescent paint. Scientists create this "coloring paint," or "probe," by attaching fluorescent labels to the DNA itself.
Our DNA is made up of two strands that fit together, like the teeth of a zipper. What scientists do is, they first separate these two strands by using a probe that they have made, and the DNA in the sample they want to test. They make this probe to match the DNA sequence they are looking for, that is, the exact sentence they are looking for in the instruction manual.
Then, they mix these prepared probes with a DNA sample taken from a body tissue or fluid (this is called the target). Then, if that probe goes and finds a piece of DNA that has the phrase it's looking for, it will stick to it (hybridize). Because of those shiny labels, that piece of DNA will glow in a beautiful color. When the pathologist looks at it with a special microscope, these shiny spots will be beautifully visible. Then he can understand whether the relevant information is there and how much of it is there. Isn't it amazing?
Genetic changes that can be detected by FISH testing
Pathologists can use this FISH test to check cells for gene mutations known to cause diseases such as cancer. It can sometimes help confirm or clarify the results of a karyotyping test, which is a test of the chromosome structure . Here are some of the specific changes that a FISH test can find:
- Amplification: This is when there are more copies of a gene than expected. It's like making a photocopy where you want to make a photocopy. Scientists can use FISH to see how many more copies of a gene there are than expected.
- Translocations/rearrangements: This is when a part of a gene or chromosome is moved to a different place than it should be. Scientists can use two colored probes to detect this. In a normal gene, the two colors of these probes should appear close together. But if the location has changed, the two colors will appear far apart.
- Deletions: Like translocations, scientists use more than one probe to find places where information is missing in DNA. Some probes will stick to the DNA in the sample, but others will not stick where they should. That's when they know that some information has been lost (deleted) at that location.
Diseases that can be diagnosed with FISH testing
Doctors can use the FISH test to detect genetic changes that can help diagnose conditions such as:
- Lymphoma
- Acute myeloid leukemia, chronic myeloid leukemia, and other types of leukemia
- Multiple myeloma
- Bladder cancer
- Glioma (a type of brain cancer)
- Mesothelioma (lung cancer)
- HER2 amplification (this is most commonly seen in breast cancer, but can also be seen in stomach and lung cancer)
- MET amplification (this is most commonly seen in lung, stomach, and esophageal cancers)
- MYCN amplification (in a type of cancer called Neuroblastoma)
- In non-small cell lung cancer , rearrangements/fusions of the genes ALK, RET, and ROS1 occur. These genes ALK, RET, or ROS1 can combine with another gene to cause cancer.
How do I prepare for a FISH test?
How you prepare for a FISH test depends on the type of sample your doctor takes from you.
- For prenatal testing: Your doctor will perform a special test called amniocentesis .
- For preimplantation genetic testing (PGD or PGS): A small sample of cells from several embryos is taken for testing. This is usually done a few days after ovulation.
- If your doctor suspects that you or your child has a disease caused by a chromosomal abnormality or gene mutation: This can be checked with a simple blood test .
- To detect cancer or genetic mutations in cancer cells (molecular testing): You will need to have a biopsy (tumor or bone marrow biopsy) , which is a sample of tissue or bone marrow.
- To diagnose or monitor bladder cancer: Sometimes a FISH test is done on a urine sample .
Of these tests, only a biopsy usually requires special preparation. Since most biopsies are done under anesthesia, you should follow your doctor's instructions on how to prepare.
How do pathologists perform this FISH test?
For a FISH test, the pathologist or laboratory technician will follow these steps:
1. Creating probe(s): In this, they select DNA fragments that match the DNA sequence they are looking for. Then, they make small cuts in that DNA and add fluorescent labels.
2. Denaturing the probe and target: This refers to separating the double bonds between the probe and the DNA sample being tested.
3. Hybridization: When probes are mixed with a DNA sample taken from a body tissue or fluid, the probes attach to the DNA sequences they are looking for.
4. Checking the results: They use a special fluorescent microscope to see where the labels glow in the sample.
The pathologist will then report these results to your doctor .
What are the results of a FISH test?
The type of results you get from a FISH test depends on the type of test you have. A positive FISH test means that there is a chromosomal or genetic abnormality in the cells in the sample. It's best to talk to your doctor about what the results will look like and what they mean.
What happens if a FISH test is positive?
If your FISH test is positive, your doctor will explain what it means and what your options are. If the test was done to find genetic mutations in a cancer, there may be targeted therapies that target that specific mutation. So it's important to talk to your doctor without panicking.
How long does it take to get the results of a FISH test?
It can take anywhere from one to four weeks to get the results of a FISH test. Your doctor will tell you when to expect the results and how to find out.
When should I contact my doctor?
If you have any questions about the test or the results you received, don't hesitate to talk to your doctor. They will explain everything to you.
Finally, the most important message
Waiting for the results of genetic tests can be scary, anxious, and sometimes even a little overwhelming. You may be waiting for an answer. This FISH test is a technology that helps you find those answers, like a "highlighter" that finds and colors the information you need .
The answers you get may not be what you expected, but they will help you understand your situation and what your options are. From there, you and your doctor can work together to develop the best plan for moving forward.
Remember, it's very important to ask your doctor for clarification on anything you think about the test, why it's being done, and what the results mean.
` FISH test, genetic testing, chromosomes, DNA, cancer, genetic mutations, prenatal testing
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