Fluorescence in situ hybridization (FISH)

FISH combines the methods of classical cytogenetics and molecular genetics. It is therefore also referred to as molecular cytogenetics.

FISH can be used to detect gene or chromosome abnormalities directly in tissues, cell nuclei or chromosomes. Specific, synthetically produced fluorescent dye-labeled oligonucleotides serve as probes to detect minute chromosomal regions that can be analyzed with a fluorescence microscope. The fluorescence in situ hybridization method can be performed on metaphase chromosomes and on interphase nuclei.

How does fluorescence in situ hybridization work?

In FISH, DNA probes labeled with a fluorescent dye bind to the appropriate specific regions of chromosomes, which are visualized microscopically as fluorescent signals after attachment.

What can be examined with FISH?

FISH can be used to detect the smallest losses and gains of chromosomal material (so-called microdeletions and duplications) as well as translocations, gene fusions and inversions. Furthermore, probe localization and unclear chromosomal alterations can be characterized on chromosomes in metaphase.

When is FISH performed?

FISH is performed in case of e.g. suspicion of

• a microdeletion syndrome
• a numerical chromosomal change
• a structural chromosomal change

In tumor cytogenetics, FISH is used to complement conventional chromosome analysis. FISH is also used to detect submicroscopic chromosomal alterations (deletions, inversions), specific translocations, and numerical and structural chromosomal alterations. It therefore plays an important role in the initial diagnosis and classification of hematological diseases according to the WHO classification. For follow-up, FISH can be used when a cytogenetic aberration is found in the initial diagnosis of a hematologic neoplasm for which a specific FISH probe is available.