Chromosomes : Chromosomal genetic tests analyze whole chromosomes or long lengths of DNA to see if there are large genetic changes, such as an extra copy of a chromosome, that cause a genetic condition. Proteins : Biochemical genetic tests study the amount or activity level of proteins or enzymes; abnormalities in either can indicate changes to the DNA that result in a genetic disorder. Topics in the Genetic Testing chapter What is genetic testing? What are the different types of genetic tests?
What are the uses of genetic testing? How is genetic testing done? What is informed consent? How can I be sure a genetic test is valid and useful? Therefore, it is important for patients and their families to ask questions about the potential meaning of genetic test results both before and after the test is performed. A positive test result means that the laboratory found a change in a particular gene, chromosome, or protein of interest.
Depending on the purpose of the test, this result may confirm a diagnosis, indicate that a person is a carrier of a particular genetic variant, identify an increased risk of developing a disease such as cancer , or suggest a need for further testing.
Because family members have some genetic material in common, a positive test result may also have implications for certain blood relatives of the person undergoing testing. It is important to note that a positive result of a predictive or presymptomatic genetic test usually cannot establish the exact risk of developing a disorder. Also, health care providers typically cannot use a positive test result to predict the course or severity of a condition.
Rarely, tests results can be false positive, which occur when results indicate an increased risk for a genetic condition when the person is unaffected.
A negative test result means that the laboratory did not find a change that is known to affect health or development in the gene, chromosome, or protein under consideration. This result can indicate that a person is not affected by a particular disorder, is not a carrier of a specific genetic variant, or does not have an increased risk of developing a certain disease.
It is possible, however, that the test missed a disease-causing genetic alteration because many tests cannot detect all genetic changes that can cause a particular disorder. Further testing, or re-testing at a later date, may be required to confirm a negative result. A couple plans to start a family and one of them or a close relative has an inherited illness. Some people are carriers of genes for genetic illnesses, even though they don't show signs of the illness themselves.
This happens because some genetic illnesses are recessive. This means they cause symptoms only if a person inherits two copies of the problem gene, one from each parent.
Children who inherit one problem gene from one parent but a normal gene from the other parent won't have symptoms of a recessive illness. A parent already has one child with a serious birth defect. Not all children who have birth defects have genetic problems. Sometimes, exposure to a toxin poison , infection, or physical trauma before birth causes a birth defect. Often, the cause isn't known. Even if a child has a genetic problem, it might not have been inherited. Some happen because of a spontaneous error in the child's cells, not the parents' cells.
A woman has had two or more miscarriages. Severe chromosome problems in the fetus can sometimes lead to a spontaneous miscarriage. Several miscarriages may point to a genetic problem. A woman has delivered a stillborn child with physical signs of a genetic illness. Where necessary, information that can identify you, such as your name and address, is removed. Your data can only be accessed by approved staff. If you have a genetic test including whole genome sequencing on the NHS, it's not possible to stop your data being stored and shared.
If you have already opted out of data from your health records being shared , this does not apply to your genetic test data. Find out more about what data about you has been stored and how it is used. The NHS is responsible for your genetic data. Page last reviewed: 03 September Next review due: 03 September Genetic and genomic testing.
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