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Molecular Cytogenetics Services |
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| Test Information | |
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* Prenatal chromosome studies
* Pediatric/Reproductive Chromosome Studies
* Cancer Chromosome Studies
* Fluorescence In Situ Hybridization (FISH) Testing
* Array Comparative Genomic Hybridization (aCGH) Analysis
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| Prenatal chromosome studies | |
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Amniotic fluid cytogenetic evaluation is appropriate for indications of advanced maternal age and
other genetic indications at 13-18 weeks gestation (occasionally later for ultrasound findings of
anomalies). Supply 15-20 ml of amniotic fluid in a sterile container. Please supply clinical
indication. Average turn-around-time 8 days.
Chorionic villus cytogenetic evaluation is appropriate for indications of advanced maternal age
and other genetic indications at 10-12 weeks gestation. We need 15-40 mg of villi. Please supply
clinical indication. Average turn-around-time 4~6 days.
Product of conception cytogenetic evaluation is appropriate in cases with multiple fetal loss or
to rule-out a chromosomal cause of fetal loss. We need samples preferably including both placenta
and fetus proper. Place sample in sterile mammalian culture medium (or if not available in a balanced
salt buffer, i.e. sterile Hepes or Hanks buffer; or sandwiched between moistened saline gauze
pads—do not immerse in saline). Average turn-around-time two weeks.
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| Pediatric/Reproductive Chromosome Studies | |
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Cytogenetic evaluation of stimulated blood is appropriate for patients in whom constitutional
structural or numerical chromosome abnormalities are suspected. This includes: Multiple
congenital anomalies or dysmorphic features, failure to thrive, developmental delay, unexplained
mental retardation, family history of a chromosome abnormality, primary or secondary amenorrhea,
couples experiencing multiple pregnancy losses or infertility, etc.
Supply 3-7 ml of blood in sodium heparin vacutainer. Please supply clinical indication. Average
turn-around-time 5~7 days.
Cytogenetic analysis from skin biopsies is indicated for suspicion of mosaicism and such cases as
Pallister-Killian syndrome. We need a sterile punch biopsy including some dermal tissue. Place
sample in sterile mammalian culture medium (or if not available in a balanced salt solution or
between saline-moistened gauze pads—do not immerse in saline). Please supply clinical indication.
Average turn-around-time two weeks.
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| Cancer Chromosome Studies | |
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Bone marrow cytogenetic evaluation is considered appropriate for patients with neoplastic or
pre-neoplastic hematological disorders. Supply 1-2 ml of bone marrow aspirate in sodium heparin
anticoagulant sterile vacutainer. Please supply clinical indication. Average turn-around-time
4~7 days (longer for B-cell malignancies).
Cytogenetic evaluation of lymph nodes, spleen, or solid tumor samples is appropriate in patients
where neoplastic or pre-neoplastic cells are suspected to be present in the biopsied sample.
Supply 0.3-1 cubic centimeter sample submerged in sterile culture medium (or a balanced salt solution).
Please supply clinical indication. Turn-around-time varies by specimen (from 5 days to 15 days).
Cytogenetic evaluation of unstimulated blood samples is appropriate in patients with suspected somatically
acquired hematologic malignancy where sufficient neoplastic or pre-neoplastic cells (blast cells) are
detected in peripheral blood. If the neoplasm is of lymphoid origin then stimulation is needed for
B-cells (Pokeweed or LPS) OR T-cells (PHA).If the blast count is low in the blood, no cytogenetic
results may be possible. Supply 5-10 ml of blood in sodium heparin anticoagulant sterile vacutainer.
Please supply clinical indication. Average turn-around-time three days (longer for B-cell malignancies).
Specialized high resolution, FISH, and other banding methods may be used to detect small structural
deletions, duplications, or translocations. FISH may be used to supplement this for
microdeletions/microduplications.
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| Fluorescence In Situ Hybridization (FISH) Testing | |
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FISH testing extends routine cytogenetic banding methods by resolving ambiguous diagnosis and
providing a new tool to diagnose submicroscopic abnormalities. FISH is a relatively simple,
fast, and reliable procedure. Depending on the sequence complexity of labeled DNA probe and
the content of tested specimen, FISH has variable signal sensitivity and spatial resolution.
Hybridization probes range from very small DNA fragments (500 bp) to large Yeast Artificial
Chromosomes (YACs) or Bacterial Artificial Chromosomes (BACs). The spatial resolution measured
by the closest separable signals could range from 5 Mbp on metaphase chromosomes to 100 Kbp on
interphase chromatins. The most important features of FISH techniques are its applicability on
different specimens and its utilization on the simultaneous detection using multiple probes.
Specimens that can be used for FISH include peripheral blood cells, cultured cell lines, bone
marrow cells, paraffin-embedded tissue sections, and frozen tissues.
Applications of FISH for hematological disorders include delineation of chromosomal numerical
abnormalities; detection of specific translocations such as those involving immunoglobulin genes
in lymphomas, and other translocation seen in leukemias; determining degree of engraftment
following sex-mismatched bone marrow and cord blood transplants; determining the origin of specific
translocations and marker chromosomes using paint probes in cases where G-banding cannot identify
the origin; and revealing cases with gene amplification.
Applications of FISH for constitutional abnormalities include detection of origin of marker chromsoomes,
delineation of subtle rearrangements, assaying for deletions and duplications in cetain syndromes, and
chromosomal rearrangements/deletions on the subtelomeric regions. Examples include: Williams-Beuren
syndrome (7q11.2), DiGeorge/Velocardiofacial/CATCH 22 (22q11.2), Prader Willii and Angelman syndrome
(15q11.2), Smith Magenis (17p11.2), Miller-Diecker/Lissencephaly (17p13), STS/Steroid sulfatase/Ichthyosis
(Xp22.3), Kallman (Xp22.3), XIST for markers to determine presence of X inactivation gene in Turner Xq13,
Y probes for sex reversal or other sex chromosome abnormalities (e.g. Turner with marker), and
Charcot-Marie-Tooth disease.
Sample submitted is usually the same sample as routine G-banding. Please supply clinical indication.
Turn-around-time varies by specimen (from 1~2 days for interphase FISH and to 4~15 days for metaphase
FISH).
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| Array Comparative Genomic Hybridization (aCGH) Analysis | |
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aCGH is a newly developed technology for a whole genome screening of segmental copy number
changes. This test is currently under development in the laboratory. Please contact the laboratory
director for the sample requirement, array format, and clinical applications.
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