Laboratory Results: In-Situ-Hybridization (ISH)

Laboratory results: In-Situ-Hybridization (ISH)

In-situ hybridization - also known as FISH (fluorescence in-situ hybridization) or CISH (chromogen-in-situ hybridization) - is a special medical-diagnostic procedure in which the genetic material of body cells or tissues is examined. In particular, with this examination method changes in the human genetic material (DNA) can be used to clarify hereditary, infectious and tumor diseases.

The main area of application of in-situ hybridization is the further diagnostic work-up in the context of congenital, genetic diseases, viral infections of cells and tissues, malignant tumor diseases, leukemia (malignant diseases of the blood and bone marrow) and malignant lymphomas (malignant diseases of the lymphatic system).

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• What is the laboratory procedure of in situ hybridization (ISH)?
• How does a FISH examination work?
• For which diseases is an ISH examination carried out?

What is the laboratory procedure of in situ hybridization (ISH)?

In-situ hybridization is a special medical diagnostic procedure in which the genetic material of body cells or tissues is examined directly on these structures.

The basis of the genetic material is a special, highly complex and long-chain molecule:

the "DNA" (deoxyribonucleic acid)

In humans, the genetic material made up of double-stranded DNA (two complementary strands) is located in the nucleus of all body cells, whereby all body cells of an individual each have identical genetic material. In addition, the exact composition of each person's individual genetic makeup is unique - comparable to the fingerprint, which is also unique for each person.

For this reason, the genetic material is also called

So-called “genetic code” is called because the blueprint of all body structures of a person is, so to speak, encrypted, mapped, saved and subsequently also passed on

Within the cell nuclei of the body's cells, the DNA is in a special order known as

• "Chromosomes" (hereditary bodies) is called. Chromosomes always occur in pairs in human body cells, with one inherited from the mother and the other from the father. In this sense, all human body cells contain a total of 46 chromosomes - 22 pairs of so-called autosomes and one pair of so-called sex chromosomes.

• The chromosomes themselves largely consist of DNA, with individual sections of the DNA sequence being referred to as “genes”, provided that they can be assigned a specific function with regard to the structure and function of the body. The sum of all genes is called

  "Genome" of the human being

Using the laboratory process of in-situ hybridization, certain areas of the genome can be visualized directly in cells and tissues. This means that the genetic material (DNA) is made visible directly in the nucleus of the cells and then examined and evaluated under the microscope. The name of this laboratory procedure is derived from this principle:

“In-situ” means “directly in the structure to be examined”

How does a FISH examination work?

The following components are required to perform an in-situ hybridization:

• a suitable test material (cell or tissue samples),
• appropriate equipment for the preparation of the ISH preparations and
• a detection system (microscopy system) to display (make visible) the genetic material in the cell nuclei.

After the examination material has been obtained, the cell or tissue material must be processed:

• Cell material is spread thinly on thin glass slides (microscope slides).
• In the case of tissue samples, histological preparation techniques are used to produce thin section specimens, which are also applied to microscope slides.

Following these preparation steps, the preparations are coated with so-called denaturing steps to obtain single-stranded DNA

“Gene probes” - these are also denatured, single-stranded DNA sequences that attach to the target sequences (if present in the test material) - in other words: “hybridize”

So that the hybridization products can subsequently be made visible for the evaluation, the DNA probes are marked either directly or indirectly with special dyes. With the dyes there is

• on the one hand fluorescence staining, whereby special fluorescence microscopes have to be used for the evaluation of corresponding preparations. For this reason, this staining method is also called

  Denotes fluorescence in situ hybridization (FISH)

• on the other hand, the DNA probes can also be stained with simple chromogens (dyes), and a simple light microscope is sufficient to display and evaluate preparations made in this way. This technique is called

  Chromogen In Situ Hybridization (CISH)

For which diseases is an ISH examination carried out?

The main area of application of in-situ hybridization is the further clarification within the framework of

• congenital, genetic diseases,
• Virus infections of cells and tissues,
• malignant tumor diseases,
• Leukemia (malignant diseases of the blood and bone marrow) as well
• malignant lymphoma (malignant disease of the lymphatic system).

Since cell or tissue samples are analyzed as test material in in-situ hybridization, this laboratory procedure can only be carried out in appropriately equipped cytological or histological laboratory facilities.

For more information on cancer, see Cancer.