Molecular Test Detection

Test : Chromosome In Situ Hybridization


Indications : FISH was originally employed to detect 22:9 translocations. The test is mostly employed in the case of parents who already have a child with developmental disability, to help them decide on having another child. It is also employed to diagnose genetic abnormalities in children.

FISH techniques are also employed to diagnose and determine prognosis and remission in those with certain types of cancers.

To carry out FISH, a synthesized, labeled DNA sequence (probe) is employed as a probe to identify a target DNA sequence in a biological sample. The target DNA and the probe are denatured and allowed to come together through annealing process. The fluorescent probe allows the visualization of the location of the target sequence through a fluorescent microscope.

Physiology : In situ hybridization is a procedure which helps us to identify the locations of specific DNA sequences on chromosomes. The procedure has acquired great levels of specificity since the time it was discovered in 1969.

Today, the procedure uses fluorescent probes and hence is commonly known as fluorescent in situ hybridization (FISH). Conventional karyotyping is useful only in detecting aberrations on larger chromosomes. FISH is much more specific, as it helps to identify aberrations involving smaller chromosomes too.

Interpretation : Aberrations involving small chromosomes and translocations within chromosomes or between chromosomes can be easily identified using FISH technique.

Some of the clinical conditions diagnosed with FISH are -

• Prader-Willi syndrome
• Angelman syndrome
• 22q13 deletion syndrome
• Chronic myelogenous leukemia (CML)
• Acute lymphoblastic leukemia
• Cri-du-chat syndrome
• Velocardiofacial syndrome
• Down syndrome

Sample : Normal chromosome number

Test Method : DNA hybridization

Related Tests : Specimen depends on the chromosome analysis required

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