When, in 1996, French nun Mariannick Caniou found out she didn’t have Huntington’s disease, the lethal, degenerative genetic disorder, she fell into a depression.
Throughout her life, she had been convinced that she would develop the illness that had killed her mother and grandmother. So convinced, in fact, that all her most important decisions had been based on that conviction: her decision not to marry, for example, or not to have children.
She didn’t regret her decision to enter the religious life, but now she had to wonder if the specter of Huntington’s had haunted that too: “Everything I had built, my life, seemed no more substantial than air.”
In the 1980s, when doctors realized they would soon have a predictive test for Huntington’s, they did not foresee stories like Sister Caniou’s. They were deeply worried about the effect the test would have on those who took it, but the focus of their worry was, understandably, those who got an unfavorable result.
They even freed up beds on psychiatric wards in anticipation of a mini tsunami of psychotic conversions. The tsunami never materialized, because those who received bad news generally coped well with it. It was the ones who got the all-clear—those like Caniou—who did not.
In the three decades since the first predictive genetic tests became available, a great deal of data has accumulated to show how people respond to knowing previously unknowable things. The rise of genetic testing has presented scientists with a 30-year experiment that has yielded some surprising insights into human behavior.
The data suggest that the vast majority react in ways that at first seem counterintuitive, or at least flout what experts predicted. But as genetic testing becomes more widespread, the irrational behavior of a frightened few might start to look like the rational behavior of an enlightened majority.
