SKY
Related Terms
Banding, cancer, chromosomes, chronic myeloid leukemia, deletions, DNA, Down syndrome, FISH, fluorescent in situ hybridization, genome, interferometer, karyotype, molecular genetics, multicolor-FISH, mutations, Philadelphia chromosome, translocation, Turner's syndrome.
Background
Spectral karyotyping (SKY) is one of many new laboratory techniques that are used to investigate the genetic makeup of an organism. Its primary focus at the present time is characterizing cancer and hereditary diseases. It can also be used to generate a deeper understanding of other diseases and indeed every process involved in the growth and function of living creatures.
SKY improves on standard microscopic karyotyping by labeling each chromosome with a unique fluorescent color or marker. Each marker gives off a different color under ultraviolet illumination, so the entire set of chromosomes, called the karyotype, can be seen at once and any piece that is out of place shows up clearly because it is a different color. SKY is one method of identifying mutations in chromosomes that cause disease.
The beginning, growth, and spread of a cancer require many separate and distinct changes from the normal functions of the cells that give rise to the cancer. Each group of cells in the body that performs the same function, called a tissue, is capable of forming a cancer. For example, skin is a tissue that forms skin cancers, and bone is a tissue that forms bone cancers. Although they share many common characteristics, each cancer is different. It can even be said that a cancer in one individual is different from the same kind of cancer in a different individual.
Changes in cells that generate a cancer include growing beyond their intended size, increasing their blood supply while growing, launching cancer cells into the bloodstream, passing through barriers that restrain normal cells, evading the body's defense mechanisms for destroying abnormal tissues, and surviving and growing in organs other than those in which they belong. Each of these changes requires a change in the genetic makeup of the cancer. These changes are all mutations in the genome of the organism.
The genome is the entire collection of genes in an organism. The human genome consists of 46 paired chromosomes that contain all the genes. There are 22 pairs of autosomes and one pair of sex chromosomes. Females have two X chromosomes, whereas males have one X and one Y. Early discoveries in the genome were limited to large changes in chromosomes that could be seen under a light microscope. For example, the Philadelphia chromosome, which is present in most cases of chronic myeloid leukemia, is a shortened chromosome 22; Down syndrome is caused by an extra chromosome 21; and Turner's syndrome is caused by an absent X chromosome.
There are many kinds of chromosomal changes that are not visible using a microscope. Some of these changes include missing pieces of chromosomes (deletion), exchanges of one piece in one location for another piece in another location, movement of one piece to a different location (translocation), and extra copies of pieces of a chromosome (duplication).
Identifying these abnormalities requires increasingly detailed knowledge of the precise molecular structure of chromosomes and the DNA of which they are made. As a consequence, increasingly refined methods of probing the fine structure of chromosomes are being developed and standardized for use in genetic research. SKY is one such method that improves upon the standard black-and-white microscopic analysis of chromosomes.
Methods
Initial successes using the genome for research began with the ability to label a single molecule with a marker or probe that attached exclusively to that molecule and to no other. The marker-plus-molecule could then be "seen" by a variety of techniques: it was radioactive or glowed under ultraviolet light or it could be separated by its electrochemical or physical properties.
Spectral karyotyping (SKY) was made possible by creating probes that attach to each chromosome. A set of human chromosomes is then mixed with a set of probes. After the bonding takes place, the chromosomes are visualized using optical techniques that can differentiate between shades of color too fine for normal vision to detect.
Spectral karyotyping differs from another similar technique only in the method for imaging the colors. Multicolor fluorescence in situ hybridization (M-FISH) sees the markers using special filters; SKY uses an interferometer and a computer that together separate the colors by their spectra and randomly assign different colors to each chromosome. An interferometer is a device that precisely identifies the frequency of a light source using the electromagnetic wave properties of light.
This technique is used to identify structural chromosome abnormalities in cancer cells and other cells involved with disease. It is more sensitive than even the highest power microscopic analysis, called karyotype banding. Karyotype banding describes the analysis of chromosomes in black and white under a microscope. Each chromosome has light and dark bands when visualized under high power. When this banding structure is different from its normal structure, it means that a piece of the chromosome is out of place. This identifies only abnormalities that are large enough to be seen under light microscopy.
Research
Cancer: The sensitivity of spectral karyotyping (SKY) and other such techniques already permits the detection of very small collections of cancer cells that remain after conventional treatment. The cancer cells have misplaced pieces of chromosome that are easily seen by SKY because they are a different color. This improves precision in predicting the course of cancers and allows for more directed secondary treatments.
Congenital diseases: SKY has also improved the detection of genetic abnormalities in children. Small chromosomal abnormalities are easily seen by SKY because they are a different color from the rest of the chromosome. Previously, black-and-white microscopy would miss these small changes.
Implications
Spectral karyotyping (SKY) is just one of many tools in the new science of molecular biology. By itself it is a small but significant contribution to the overall progress toward useful applications. It has a certain niche where it is the best technique available. Other techniques have their niches as well. Combined with the mass of related knowledge already accumulated, these techniques will move research forward and permit further discoveries, eventually producing generally applicable tools for popular use.
SKY is unique in that it is a relatively simple procedure that gives vivid and easy-to-read results. Cancer and congenital genetic diseases are its principal applications at present.
This technology is very new. Consequently efforts are currently limited to discovery and have not yet matured to the point of useful treatments. So far the most relevant use for the general population is for more specific diagnosis of congenital genetic diseases and more accurate identification of residual cancer after treatment. It can also identify specific characteristics of certain cancers, notably leukemias and lymphomas, that are related to how aggressive the cancers are and how well they respond to treatment.
Limitations
The limitations of spectral karyotyping (SKY) are simply that it is a very young technology and is only in the discovery stage. New uses will emerge as they are thoroughly researched, exhaustively tested for accuracy and effectiveness, and standardized for general use. SKY is representative of the many new tools being developed to explore genetic structure and function. Each represents a step forward, and each will find applications for which it is best suited.
SKY is limited to abnormalities that are visible under a light microscope. Many other abnormalities of the genome occur at a molecular level and require far more sophisticated methods. Furthermore, SKY is not a treatment, only a more precise method of diagnosis. On the other hand, it is relatively simple and inexpensive, does not require costly laboratory equipment, and can be performed in community facilities.
Future research
Most research in the near future will likely be discovery rather than application. Spectral karyotyping (SKY) does not change anything and is therefore not a treatment. It will find its uses, along with the many other cytogenetic tools being developed, in identifying the life processes that cause disease and allow living organisms to thrive and grow.
Author information
This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).
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