Fluorescence in situ hybridization (FISH)


August 29, 2023

Fluorescence in situ hybridization (FISH) is a laboratory test used in pathology to detect and localize the presence or absence of specific DNA sequences on chromosomes. It works by using fluorescent probes that bind to only those parts of the chromosome that match or are complementary to the probe. It is commonly used in the diagnosis of cancer and certain genetic syndromes.

How does fluorescence in situ hybridization work?

  1. Probe preparation: A fluorescent probe is designed to match the specific DNA sequence of interest. This probe is then labeled with a fluorescent dye. Different probes can be labeled with different dyes to detect multiple targets simultaneously.
  2. Sample preparation: The DNA in the sample (such as cells from a blood sample, a biopsy, or tissue sections) is denatured, meaning it’s heated to separate the double-stranded DNA into single strands.
  3. Hybridization: The fluorescently labeled probe is applied to the sample, where it seeks out and binds (hybridizes) to its complementary DNA sequence within the genome.
  4. Washing: After hybridization, the sample is washed to remove any excess probe that hasn’t bound to its target DNA. This step helps to reduce the background signal and improve the specificity of the detection.
  5. Detection: The sample is examined under a fluorescence microscope. The probes that have bound to specific DNA sequences will fluoresce, and their location can be visualized and analyzed.

Why is this test performed?

Fluorescence in situ hybridization’s ability to provide precise genetic information at the cellular level makes it an invaluable tool in the diagnosis and management of cancers and genetic diseases.

  • Detection of chromosomal abnormalities: FISH can identify specific genetic mutations, deletions, duplications, and translocations associated with various genetic diseases and conditions, including cancers. For example, it’s widely used to detect the Philadelphia chromosome in chronic myeloid leukemia (CML), a specific translocation between chromosomes 9 and 22.
  • Cancer diagnosis and prognosis: By identifying genetic changes specific to certain types of cancer, FISH helps in diagnosing the disease, determining its prognosis, and selecting appropriate therapies. For instance, it’s used to detect HER2/neu amplification in breast cancer, which can influence treatment decisions.
  • Genetic diseases: FISH is used in the diagnosis of genetic conditions, such as Down syndrome, by detecting the presence of an extra copy of chromosome 21.
Fluorescence in situ hybridization
Fluorescence in situ hybridization (FISH). The probes are seen as green and red dots within the blue nucleus of the cell.

About this article

Doctors wrote this article to help you read and understand your pathology report. Contact us if you have questions about this article or your pathology report. For a complete introduction to your pathology report, read this article.

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