Huntington's disease (HD) is relatively rare among monogenic disorders, in that it has a penetrance of virtually 100%, ie. every individual who carries a copy of the mutant gene, will go on to develop the disease. The serious nature of the disease and the implications of genetic testing for the presence of disease-associated mutations, combined with the adult onset of symptoms in affected individuals, has in the past argued against predictive genetic testing among the under eighteens. A new study by an Australian group, published in the American Journal of Medical Genetics, reports on the findings from interviews with eight young individuals aged between 17 and 25 about their experiences of genetic testing for HD [Duncan RE et al. (2007). Am J Med Genet Part A 143A: 1984–1989].
When asked about their life prior to genetic testing, the participants reported a range of risk-taking behaviours and a general assumption that they would in the future prove to be mutation carriers, although all were aware the probability of this was 50%. All of the participants went on to have genetic testing, and two of the eight proved to be carriers. Interestingly, both carriers and non-carriers reported reduced levels of anxiety and a sense of being able to ‘move forward’ and get on with their lives following testing, although two of the non-carriers reported difficulties in adjusting to the realization that, contrary to their expectations, they would not go on to develop HD.
Comment: The authors note the similarity of their results and those of earlier researchers, who had not restricted their analysis to younger individuals; they also acknowledge the significant limitations of their very small study. However, the work adds an interesting perspective to the debate about appropriate ages for genetic testing for serious disease; perhaps most notably, “Not one of the young people interviewed regretted undergoing predictive testing”. They observe that genetic testing among younger people may actually alleviate existing harms, whereby the fear or assumption of carrier status presents an effective barrier to the normal progression into independent adult life. This finding would certainly suggest that testing of competent younger people below the legal age of majority for HD and other diseases may indeed be appropriate in some cases.