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Genetic testing looks for changes or differences in a person’s genes. Not all genetic changes are harmful. Some can have beneficial, neutral, or uncertain health effects. Genetic changes that have the potential to cause harmful health effects are called mutations.
Some mutations result in a disorder that means there is a higher-than-normal risk of certain types of cancer. Mutations that cause many of the known hereditary cancer syndromes have been identified. Testing can confirm whether a condition is the result of a hereditary condition. Genetic testing may also determine whether family members without signs of illness have inherited the same mutation.
A karyotype is a picture of the chromosomes — thread-like structures in cells that hold the genes.
It can show:
FISH testing uses fluorescent probes to look at specific areas of the chromosomes.
It can show areas of 1 or more chromosomes that are missing, extra, or out of the normal order. These changes may be too small to be seen on a karyotype.
FISH testing finds specific changes in chromosomes that the fluorescent probes are set to look for. It does not examine all the chromosomes.
This test looks at all the chromosomes for any missing or extra pieces.
It can show very small missing or extra chromosome pieces that the karyotype or FISH test might miss.
It does not show chromosome pieces that are out of the normal order.
Deletion/Duplication testing looks for any missing or extra pieces within a specific gene.
It can find missing or extra pieces of DNA that are usually too small to be seen with karyotype, FISH or SNP chromosome microarray testing.
Each person inherits 1 copy of each gene from his or her mother and 1 from his or her father. Usually, these genes both work the same way.
They are “turned on” or “turned off,” depending on the type of cell they are in. But for some genes, only 1 copy is turned on or off. This happens in a process called “methylation.” Methylation testing checks to see if the process is happening correctly on a specific gene or chromosome.
Methylation testing can find changes in the pattern of methylation of a specific chromosome area or gene the test is set up to look at.
Typically, a person inherits 1 copy of each chromosome from his or her mother and 1 copy from his or her father. But a person can have 2 copies of an entire chromosome or two copies of a specific part of a chromosome that both come from 1 parent. This is called uniparental disomy or UPD.
This test finds uniparental disomy on the specific chromosome or chromosome area being tested.
Sequencing reads the code for the DNA letters (A, T, C, G) that make up the genes. It looks for any changes from the normal code.
DNA sequencing can be done on 1 gene or on multiple genes.
Genomic sequencing is when all a person’s genes are being tested at once.
This test can show if there is a change in the order of DNA letters that make up 1 or more genes.
Sequencing can also show if 1 or a few of the DNA letters are lost or if there are extra letters.
Mostly, this test does not show larger DNA areas that are missing, extra, or out of the normal order.
Reviewed: June 2018
A genetic counselor, a health care professional with advanced training and experience in medical genetics and counseling, can help families find answers.
Learn more about genetic counselors
Cancer predisposition means some people have an increased chance of developing cancer because of a genetic condition.
Learn more about cancer predisposition