The science and practice of testing for Huntington's disease
What if I decide not to be tested?
Many individuals decide that they would rather live at risk than discover that they have an HD allele. For some, the chances of experiencing the relief of having no HD-alleles are outweighed by the risk of finding out the opposite - that if they live long enough they are very likely to develop symptoms of HD. The decision to be tested is a personal choice and should be approached very carefully. Counseling during and after the testing process is an essential part of preparing the individual for the potentially life-changing test results they will receive. It is common even for those individuals who learn that they do not have an HD-allele to experience high levels of anxiety after learning their results. Hence, the process is intentionally designed to give the people involved plenty of time to rethink their decision. Many individuals choose to be tested but never return to hear the results.
So what happens if you choose to live at-risk, without undergoing testing? Most individuals with the HD allele develop symptoms during the third, fourth, and fifth decades of life. A smaller percentage of individuals develop HD in their 60’s and afterwards. Figure S-4 lists the probability that you have the HD allele if you are 50% at-risk and remain asymptomatic at a given age. These data were compiled by taking all the at-risk individuals in a specific age group who show no symptoms (are asymptomatic) and then calculating the percentage of these individuals that developed HD later in life. For example, of the individuals who were asymptomatic at age 50 years, 31.5% developed HD at some later age.
This figure pertains to at-risk individuals - those who have a parent with HD - and therefore assumes a 50% probability of actually inheriting the HD allele. However, as one gets older and remains asymptomatic, the odds of having the allele decrease (as implied by the graph). This pattern arises because most individuals with the allele will already have developed HD by a given age. If a person has already lived a certain number of years without developing symptoms, then chances are relatively high that this person may be in the group that does not have the allele. Conversely, chances are lower that this person is in the group that does have the HD allele. Please note: the information in this graph is not, in any way, a substitute for a genetic test. The numbers do not represent exact predictions for the probability that an individual who is asymptomatic at a given age will develop HD later in life. However, the figure gives a rough estimate of how this probability changes over the course of a lifetime.
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