Huntington's Disease

Implications of Predictive Testing

Although the discovery of the HD gene has facilitated predictive testing, the disease remains without a cure, and no treatment is currently available to slow or alter the disease's progression. Therefore, the availability of such testing continues to be associated with numerous emotional, practical, and ethical concerns. This highlights the necessity of appropriate genetic counseling and support.

Certain factors may complicate the use of predictive genetic testing for HD. For example, confirmation of the diagnosis in affected relatives is important, since HD may be misdiagnosed, particularly in new, isolated instances in which there was no previous family history. A number of dominantly inherited neurodegenerative diseases may closely mimic HD, potentially leading to improper diagnosis. (See "Differential diagnosis.")

Questions remain concerning the implications of results obtained by predictive testing. As mentioned previously, DNA linkage analysis may have varying degrees of accuracy. Testing with direct mutation analysis may have uncertain implications if an intermediate number of CAG repeats is present. Even confirmed positive results do not currently provide accurate information concerning the approximate age at onset, clinical severity, or rate of disease progression.

Individuals at risk for HD who are interested in the possibility of genetic testing are referred to specialized, designated testing centers that have staff with the necessary expertise and appropriate psychosocial counseling experience. Individuals who are considered "at risk" for HD may have a parent who has HD or is known to carry an HD gene mutation. Those considering genetic testing require sufficient information and appropriate counseling concerning the limitations of genetic testing, their potential level of risk, and the possible implications of results including negative, positive, or inconclusive findings.

During such pre-test counseling, individuals are provided with information about HD and its various symptoms and findings, details on how predictive genetic testing is conducted, and information regarding additional diagnostic screening procedures.

Genetic counseling concerning the implications of positive or questionable results should address a number of essential areas, including:

• Long-term emotional and lifestyle issues
• Confidentiality concerns (including the fact that patient confidentiality laws are governed by individual states)
• Possible effects in the areas of health insurance, life insurance, and employment
• Practical, emotional, and personal impact on spouses as well as relatives who themselves may be at risk including children, parents, or other relatives
• Family planning

Individuals who are considering such testing may wish to have a relative or close friend accompany them to their counseling sessions.

In summation, it is essential that pre-test counseling provide individuals with sufficient information on which to base an informed decision concerning whether to go forward with testing. A decision to receive genetic testing must be carefully considered and made solely by the individual.

Predictive testing may be associated with a number of additional ethical issues, such as complex situations in which close relatives may not be willing to provide blood samples or when diagnostic confirmation of HD is required concerning a relative who is against receiving clinical assessment, such as neurologic testing. Ethical and legal views typically hold that an individual's right to receive predictive testing for HD is outweighed by his or her family member's right for privacy and confidentiality.

Because transient or temporary depression is common among those at high risk for HD, pre-test screening may include psychological screening to help identify individuals who are most likely to require strong emotional support. Those with a history of severe psychiatric illness, who are at risk for major depression, or who have suicidal tendencies may consider or be asked to postpone genetic testing. In such cases, psychiatric treatment is typically suggested to help stabilize individuals before genetic testing for HD. Pre-testing also requires a thorough neurologic evaluation to determine whether those considering genetic testing are demonstrating any clinical signs of HD. At-risk individuals must be informed that the presence of certain neurologic signs may suggest the diagnosis even before predictive genetic testing is conducted. (See "Clinical evaluation.")

When predictive genetic testing is indeed performed, it is essential that appropriate counseling and supportive services be available for tested individuals. Follow-up is recommended regardless of whether test results are positive, inconclusive, or negative. Test results are strictly confidential and not provided to anyone other than the tested individuals without their written consent.

Established testing and counseling guidelines help to address the complex outcomes of predictive testing for HD, including emotional, practical, ethical, and legal issues. Individuals who are considering such testing may obtain such information from testing centers or various patient organizations.