Administrative Office
St. Joseph's Hospital Site, L301-10
50 Charlton Avenue East
HAMILTON, Ontario, CANADA L8N 4A6
PHONE: (905) 521-6141
FAX: (905) 521-6142
http://www.fhs.mcmaster.ca/hrlmp/
Issue No. 49
QUARTERLY NEWSLETTER
September, 1999
New Molecular Cytogenetics Facilities - SKY and
Microdissection
New developments have been initiated at the Hamilton Regional Cytogenetics Services. Two novel and
sophisticated molecular cytogenetic facilities, spectral karyotyping (SKY) and microdissection, have been
recently set up at McMaster Division HHSC. These two facilities will expand our cytogenetic diagnostic
capacity and will also improve our present ability to make diagnosis more accurately and more efficiently.
Cytogenetic diagnosis consists of tissue or cell culture, preparation and analysis of chromosomes
(karyotyping), and clinical interpretation of a cytogenetic finding. In recent years, technical advances in
chromosome staining and analysis have dramatically improved the accuracy and sensitivity of cytogenetics.
Developed in 1970, G-banding has been the gold standard in clinical cytogenetics. It is easy to use, highly
reproducible, and inexpensive. It involves trypsin digestion of metaphase chromosomes, followed by Giemsa
staining. It produces a differential banding pattern along the length of a chromosome, allowing for
identification of individual chromosomes. G-banding has been routinely used for diagnosis of numerous
numerical and structural chromosome anomalies such as Down syndrome, Klinefelter syndrome, and Cri-du
chat syndrome.
However, G-banding has limitations. Firstly, it cannot identify a chromosome rearrangement without a
distinctive band pattern, such as translocations involving distal G-negative bands, small insertions, or
markers. Secondly, it has a limited resolution of one band (about 2000~4000 kb in size), so it cannot be
used to detect the very small deletions implicated in many microdeletion syndromes. Finally, it cannot be
used to study interphase cells.
In the last ten years, a new molecular cytogenetics technology, called fluorescence in situ hybridization
(FISH), has rapidly developed and revolutionized chromosome diagnosis. FISH involves labeling a specific
DNA probe with a fluorochrome, hybridizing the probe to metaphase chromosomes or interphase nuclei and
visualizing the hybridized signal on a fluorescence microscope. Depending on the probe used, a
chromosome, a chromosome arm, a region or even a single gene can be selectively highlighted. Multiple
color FISH can be used to visualize several probes in a single test. At 1 kb of resolution ( vs. 2000~4000 kb
with G-banding), FISH can detect fragments of genes and it can also be used to study interphase cells.
Since 1993, our services have been performing FISH diagnosis for chromosome aberrations, particularly
translocation, duplication, and many microdeletion syndromes. We currently have probes for a number of
syndromes, including DiGeorge/Velocardiofacial, Prader-Willi, Angelman, Williams, Wolf-Hirschhorn, SmithMagenis, Miller-Dieker syndromes. However, so far our FISH has been limited to metaphase chromosomes
and a maximum of three colors (or probes) in a single test.
SKY
Our new SKY equipment can display and identify all 24 human chromosomes (22 autosomes plus X and Y
chromosomes) in different colors in one analysis. It will be possible for us to:
1.
2.
3.
4.
definitely identify cryptic translocations in apparent normal chromosomes,
identify subtle rearrangements, rings, and markers,
identify complex aberrations in constitutional and cancer cytogenetics, and
provide rapid (overnight) prenatal diagnosis of trisomy 21(Down) syndrome, trisomy 13 syndrome,
trisomy 18 syndrome, 45,X (Turner) syndrome, 47,XXY (Klinefelter) syndrome.
Because of a current high cost (~$150/test) for reagents and increased technical/analysis time, we will be
introducing SKY only for priority cases at first.
MICRODISSECTION
Microdissection is a new molecular cytogenetics system and is the only way to make an accurate diagnosis
in some complex and rare chromosome aberrations. It is also the only way to generate chromosome regionspecific FISH painting probes or DNA sequences. It can be highly sensitive in detecting an aberration even
when it presents in very small proportion of cells, and extremely accurate in defining what chromosome
region is involved.
Microdissection is a multi-step procedure, including chromosome preparation, G-banding to identify a target
chromosome, dissecting a target chromosome using a glass needle, PCR amplification , fluorescence
labeling of the PCR products, FISH of the labeled DNA on normal chromosomes, FISH imaging and
analysis, and cloning the DNA sequences when necessary.
Microdissection will be useful in selected diagnostic cases and in research for:
1. identification of marker, small insertion, deletion, and rings,
2. identification of double minutes and homogeneous staining region in cancer specimen,
3. development of a family-specific ("private") paint probe for prenatal or postnatal diagnosis of a "risk"
chromosome,
4. development of painting probes for multicolor FISH banding,
5. isolation of chromosome breakpoint or disease causing genes, and
6. molecular cytogenetics of gene amplification in cancer.
These two new molecular cytogenetic systems, SKY and microdissection, in conjunction with our routine
cytogenetics procedures, will have a significant impact on our genetics services, clinical management and
technological development.
It will take approximately 6 to 12 months to train technologists and optimize protocols before these two new
molecular cytogenetics services are fully available. A regional announcement will be made at that time.
Jie Xu, Cytogeneticist
Viola Freeman, Laboratory Manager
Ron Carter, Director, Cytogenetics
Human Genetics
Hamilton Health Sciences Corporation
MUMC Campus
The Hamilton Regional Laboratory Medicine Program is a collaborative program of the Hamilton Health
Sciences Corporation, St. Joseph's Hospital and McMaster University.
For further information concerning the Hamilton Regional Laboratory Medicine Program contact Mrs. Sue
Friend at (905) 521-6141.
For information on Community Laboratory Services please contact Mrs. Kathy Tiers (905) 521-6052, or the
Laboratory Reference Centre contact Mrs. Barb Baltzer at (905) 521-6065 or fax to (905) 528-1464.