Presymptomatic genetic testing when no treatment is available stands in contrast to genetic testing done for the diagnosis of a current disorder. Huntington's disease (HD) is an example of a genetic disorder in which clinical manifestations begin in adulthood. Although some symptoms can be managed with medications, no treatment is yet available to alter the gradual loss of muscle control, psychiatric changes, and progressive dementia.
HD is an autosomal dominant disorder, which means that an individual with only one abnormal copy of the HD gene will develop the disease, and the children of affected individuals have a 50 percent chance of inheriting the genetic mutation. The gene abnormality occurs when a polymorphic CAG repeat sequence is expanded beyond the normal number of 10 to 29 copies. Diagnosis of HD is almost 100 percent sure when the number of CAG repeats is in the range of 36 to 121.
Individuals at risk for HD may want to undergo genetic testing to end the uncertainty of not knowing whether they will be affected. This knowledge may allow for career and life planning. However, concerns that presymptomatic diagnosis of HD would lead to serious psychological distress or suicide led to the development of testing guidelines. The standard was established that all individuals who sought HD testing should receive pretest counseling to explain the test, assess their psychological status, and
Genetic Testing: Ethical Issues
dementia neurological illness characterized by impaired thought or awareness polymorphic occurring in several forms
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