The science and practice of testing for Huntington's disease
What are the preliminary steps of the genetic testing process?
Although specific procedures vary among testing centers, genetic testing for Huntington’s disease generally involves several sessions that take place over the period of at least one month.
Step 1: Pre-test Genetic Counseling
A genetic counselor provides the individual who is considering testing with basic background knowledge about genetics, the inheritance of HD, and the testing procedure. These preliminary sessions ensure that the individual understands the clinical and psychological implications of genetic testing and is prepared to receive the test results.
Step 2: Neurological Examination
The purpose of this clinical phase is to determine whether the at-risk individual is already showing symptoms of HD. A neurologist tests body movement, reflexes, eye movement, hearing, and balance. Brain imaging scans may also be used to check for the characteristic changes in brain structure caused by HD. These clinical observations are combined with an extensive family medical history in order to yield the diagnosis. If an individual is found to be symptomatic, he/ she can either continue with the genetic testing process to confirm the diagnosis, or withdraw from genetic testing.
What is the difference between testing for HD and diagnosing HD?
Genetic testing shows whether or not an individual carries the HD allele, a mutated version of the Huntington gene. A positive test result indicates that the HD allele is present and that the individual will eventually develop Huntington’s disease. However, the genetic test is not sufficient to diagnose HD because it does not show whether the clinical symptoms are already being expressed. This information can only be obtained through the neurological exam discussed above, which is the definitive means of diagnosing or establishing the onset of HD.
Step 3: Psychological/Psychiatric Interview
In this phase, a mental health professional assesses the mental and emotional state of the individual considering testing and provides counseling support services.
Generally, there is a time interval between the preliminary sessions and the actual genetic test. This waiting period provides the individual with sufficient time to consider the implications of genetic testing and reach a final decision.
Last Modified: 9-13-02
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