Genetic testing for Huntington disease.

In 1983, Huntington disease (HD) became the first disease to be mapped to a previously unknown location on chromosome 4. This discovery meant that we could now identify whether some individuals at risk for HD would develop HD in the future using a method called linkage testing. Testing was first offered through research protocols designed to assess whether testing could be done safely in this population. Testing guidelines were soon developed by the Huntington's Disease Society of America and the International Huntington Association in collaboration with the World Federation of Neurology. The gene for HD was found in 1993, allowing for direct gene testing for the mutant HTT allele. This chapter will discuss the development of guidelines and recent revisions to the guidelines, prenatal testing, and testing in three complicated situations: (1) the testing of minors; (2) anonymous testing; and (3) testing individuals at 25% risk. Studies examining the outcomes of predictive testing will also be discussed. Outcome studies have shown that testing can be done safely in the context of testing protocols that include neurologic examinations, pretest counseling, psychiatric/psychologic assessment, results in person, and available follow-up support. It appears that anxiety and depression prior to testing are better predictors of psychologic status after testing than the test result itself.