Fluorescence In Situ Hybridization [FISH]
Fluorescence in situ hybridization is a molecular cytogenetic
technique in which fluorescently labeled DNA probes are hybridized
to metaphase spreads or interphase nuclei. Applications include
identification of structurally abnormal chromosomes, including
several of the cancer translocations, such as BCR/ABL and TEL/AML1
translocations; identification of marker chromosomes; detection
of very small deletions (microdeletions); and rapid detection
of Down syndrome and other numerical chromosome abnormalities;
and the rapid detection of sex chromosomes and the SRY gene.
FISH should be used in conjunction with G-banded chromosome
analysis.
FISH is performed
upon request when a specific numerical or structural abnormality
or microdeletion is suspected. FISH is also utilized to confirm
microdeletions identified during high resolution chromosome analysis
and to aid in identification of abnormal chromosomes. Interphase
FISH is especially useful in bone marrow / cancer analyses when
there is poor or no growth of the specimen.
Specimen requirements: FISH can
be performed on any tissue that can be cultured for chromosome
analysis and interphase FISH can be performed on any cytogenetic
sample. Follow collection and transport guidelines specific
for each tissue type. Studies requested should be indicated
at the time of sample submission.
Analysis: The standard of analysis
varies depending on the probe used. Hard copies of at least
2 cells are digitally archived for documentation.
Report: Results are come as a separate
report for most studies, and should be available within one
week of culturing. >
CPT codes: Vary according to specific
purpose.
FISH 3-5 metaphase
cells = 88272, 88271*
FISH 10-30 metaphase cells = 88273, 88271*
FISH 25-99 interphase cells = 88274, 88271*
FISH 100-300 interphase cells = 88275, 88271*
* for each probe
- so, a dual-probe assay would be 88271 X 2
FISH probes are
available for:
(New probes are always being developed, please call concerning
other conditions)
Microdeletion
Syndromes
A number of genetic
syndromes are caused by the deletion of a small region of a particular
chromosome. Often these deletions are too small to be picked
up by standard or high resolution chromosome analysis, in which
case, microdeletion syndrome probes must be used to elucidate
the chromosome abnormality. These probes are pieces of DNA specific
for the region deleted in the specified syndrome, and usually
include a control probe which identifies the chromosome of interest.
- Wolf-Hirschhorn (4p-)
- Cri-du-chat (5p-)
- Williams syndrome
(7q11.23)
- Prader-Willi syndrome
(15q11.2-q13)
- Angelman syndrome
(15q11.2-q13)
- Miller-Dieker syndrome
(17p13.3)
- Smith-Magenis syndrome
(17p11.2)
- DiGeorge and Velo-cardio-facial
syndromes (22q11.2)
- Kallman syndrome
(Xp22.3)
- Steroid Sulfatase
Deficiency (STS) (Xp22.3)
- X-Linked Ichthiosis
(Xp22.3)
- Retinoblastoma (13q14)
Trisomy Detection
and Sex Determination
Probes for chromosomes
13, 18, 21, X, Y and SRY. These probes are used to screen interphase
(uncultured) cells for trisomy 13, trisomy 18, trisomy 21, chromosome
number for sex chromosomes (X and Y) and for the presence of
the male determining gene SRY. FISH can be performed as an initial
screening test in certain high risk situations where trisomy
is suspected, such as in amniocytes from a pregnancy with an
abnormal ultrasound or uncultured lymphocytes from an infant
with ambiguous genitalia.
Results may be obtained
24 hours after receipt of the sample.
Oncology
FISH analysis is
available to rule out certain common oncology related translocations,
deletions and amplifications. This analysis is particularly
useful when a specific hematologic disease is highly suspected
(i.e. Philadelphia chromosome in chronic myelogenous leukemia)
and/or cells fail to grow in culture. FISH can be used to look
for minimal residual disease in patients undergoing treatment
or in patients thought to be going into or coming out of remission.
It can be used to detect unusual variants of the Philadelphia
chromosome translocation, and to follow bone marrow transplants
in certain patients. Since most of these oncology probes are
used on interphase cells, standard cytogenetics is still necessary
to look for other chromosomal aberrations and to detect clonal
evolution of disease, an important prognostic indicator.
Single Gene Probes (deletion or amplification)
- P58 CLK-1 Locus (1p36)
- D7S486 (7q31)
- Retinoblastoma (13q14)
- p53 (17p13.1)
- Her-2/neu (17q11.2-q12)
Enumeration probes
for all chromosomes
- Dual Color Translocation
Probes
- bcr/abl translocation t(9;22)(q34;q11.2) (both major and minor
breakpoints)
- M-bcr/abl translocation t(9;22)(q34;q11.2) (major breakpoint)
- IGH/CCND1 translocation t(11;14)(q13;q32)
- PML/RARA translocation t(15;17)(q22;q21.1)
- TEL/AML1 translocation t(12;21)(p13;q22)
Amniotic Fluid
Aneuploid detection
by FISH for chromosomes 13, 18, 21, X and Y may be indicated
in situations where there is a risk of a numerical chromosome
abnormality. This risk is usually based on abnormal ultrasound
findings. FISH may also be indicated in cases of late gestational
age when a rapid result is required. FISH should be followed
by a complete karyotype analysis and no clinical action should
be taken based solely upon FISH results. FISH is best performed
prior to 22 weeks gestation. After 22 weeks, considerable cellular
debris is present and may lead to inconclusive results. This
test must be requested at the time the sample is received so
that 3 - 5 mls of amniotic fluid can be separated for use with
this test.
Results are available
24 - 48 hours after receipt.
Newborn Screening
FISH can be performed
on peripheral blood or cord blood from newborns at risk for trisomy
13, 18, 21 or abnormalities of sex chromosome number. Blood
must be collected in a sodium heparin (green top) tube. Please
call to advise when samples are being sent for this screening.
Results are obtainable
within 24 hours of receipt.
Telomere Alteration
Testing
This test will identify
alterations in 7% to 10% of cases with moderate/severe mental
retardation (MR) and cases with multiple congenital anomalies
(MCA) with MR. The analysis involves the detection of deletions
or duplications or cryptic translocations using subtelomere FISH
probes for each chromosome.
Samples should be
collected as for high resolution chromosomes in sodium heparin
tubes. Please make sure to clearly indicate telomere analysis.
If chromosome analysis has not been done previously by GGC, please
call the laboratory before requesting.
Results are currently
taking 3 to 4 weeks, as the test is very labor intensive.
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