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Microdeletion/Microduplication Syndrome by Fluorescence In Situ Hybridization (FISH) Analysis

FISH, microdeletions, microduplications, genetic, DiGeorge Syndrome/Velocardiofacial syndrome, Prader-Willi/Angelman syndrome, Williams syndrome, Wolf-Hirschhorn syndrome, Smith-Magenis syndrome, Miller-Dieker syndrome, Kallmann Region, SRY Region, Cri-du-Chat Region

Test Codes

Please contact the Cytogenetics Laboratory if assistance with ordering in EPIC is needed.

Department

Cytogenetics

Specimen Collection Criteria

Collect: Peripheral blood in a Dark Green-top Sodium Heparin tube, or amniotic fluid or chorionic villus tissue in a sterile collection container.

A copy of the requisition must be sent with the specimen.

Physician Office/Draw Specimen Preparation

Do not freeze specimen. Maintain specimens at room temperature (20-25°C or 68-77°F) prior to courier pickup. For delays in transport (greater than 48 from the time of collection), refrigerate (2-8°C or 36-46°F) the specimen.

Preparation for Courier Transport

Transport: Peripheral blood, amniotic fluid, or chorionic villus, at room temperature (20-26°C or 68-78.8°F) or refrigerated (2-8°C or 36-46°F).

Rejection Criteria

Specimens arriving in the laboratory 4 days or more following the original collection date.

Fixed or frozen specimens. 

In-Lab Processing

Specimens are processed immediately upon receipt in the Laboratory.

Storage

Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): 48 hours
Refrigerated (2-8°C or 36-46°F): 96 hours
Frozen (-20°C/-4°F or below): Unacceptable

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days. A backup cell pellet is maintained for three weeks after the case has been signed out for all peripheral blood specimens.

Laboratory

Royal Oak Cytogenetics Laboratory

Performed

Monday – Friday, 8:00 am – 5:00 pm.
Results available within 7 days of receipt in the Laboratory.

Reference Range

Positive or negative for deletion or duplication of the gene in question.

Test Methodology

Fluorescence In Situ Hybridization (FISH) Analysis.

Interpretation

A positive FISH result indicates deletion or duplication of the targeted gene. A negative result cannot completely rule out a diagnosis due to another genetic cause or gene mutation. Chromosome microarray analysis may be recommended as a follow-up study. Any patient with a positive FISH result should be referred for clinical genetic evaluation and genetic counseling.

Clinical Utility

Several dysmorphic genetic syndromes are associated with small deletions that lead to a form of genetic imbalance known as segmental aneusomy. These are thus referred to as segmental aneusomy syndromes or contiguous gene syndromes. These deletions produce a clinically recognizable phenotype that consists of features associated with haploinsufficiency of the genes in the deleted region. Recent evidence has revealed that the chromosome breakpoints in these disorders lie within low-copy repeated DNA sequences and that aberrant recombination between nearby copies of these repetitive sequences can result in deletions that span several hundred to several thousand kilobase pairs. This research has also uncovered that this genetic mechanism can generate microduplications of the same regions (microduplication syndromes). These rearrangements are sometimes detected unequivocally with high-resolution cytogenetic analysis; however, a more definitive test is fluorescence in situ hybridization (FISH). A deletion can be identified by either metaphase or interphase FISH analysis, while duplication of the region is most often identified by interphase FISH analysis. A FISH assay for each of the following genomic disorders is offered:

Disorder	Chromosome Region	Targeted Gene or Probe
DiGeorge Syndrome/Velocardiofacial syndrome	22q11.2	TUPLE1 (HIRA)
Prader-Willi/Angelman syndrome	15q11q13	SNRPN
Williams syndrome	7q11.23	ELN
Wolf-Hirschhorn syndrome	4p16.3	WHSC1
Smith-Magenis syndrome	17p11.2	SMS
Miller-Dieker syndrome	17p13.3	LIS1

The utilization of these FISH assays requires clinical suspicion of the disorder so that the correct DNA probe is used. Other probes are available and can be run on a case-by-case basis. Please contact the lab for further details. Concurrent conventional cytogenetic analysis and/or SNP array is also strongly recommended to identify other chromosome abnormalities.

CPT Codes

88271x2 DNA probe, each.
88273x1 Metaphase analysis, 10-30 cells.
88275x1 Interphase analysis, 100-300 cells (DiGeorge/VCFS only).

Contacts

Last Updated

12/30/2022