Sir

Your Special Report 'Genetic testing for everyone' (Nature 453, 570–571; 2008) discusses the contentious issue of breaking the news about test results. Our experience of conducting genetic-testing enquiries in Colombia, which has the largest kindred in the world with familial Alzheimer's disease, indicates that individual resilience may vary greatly. Justifying relaxation of recommendations for vigilance on the basis of findings “that most people are remarkably resilient in the face of traumatic genetic test results” gives short shrift to those who are not.

When we asked a 24-year-old man whose mother harbours the highly penetrant presenilin mutation what he would do if he tested positive for the gene, he indicated that he would shoot himself in the head. Although he would probably have another 24 dementia-free years ahead of him, because the average age of disease onset in this community is 48 and variation around the mean is relatively small, the eventuality of a disease many years in the future pervaded his thinking.

Seeking predictive genetic testing can be a risky behaviour, and an individual's likely response to genetic risk is hard to foretell. Functional magnetic resonance imaging activity patterns may be able to define people who are more comfortable with risk, and genetic polymorphisms seem to contribute to risk-taking behaviour. Defining the scientific basis for how individuals handle volatile genetic information may help guide our decisions about the best setting for delivering predictive-testing news.

At what point does genetic destiny overtake the hope of beating the odds? In the Colombian families, an affected parent already sets the risk of disease at 50%, a level that in our experience creates significant anxiety but is tolerable.

Genetic testing, whether it offers a stick of dynamite or a stark warning to which we can adapt, must be backed up by reliable, accessible, up-to-date information. For example, the completion of phase III clinical trials can radically alter a bleak message detected in the genome.