But for now, when a disease is nontreatable, the burden of knowing can overwhelm the benefits. Nationwide, only 1,500 genetic counselors, most of them drawing on guidelines derived from Brandt's research, have been trained to help people assess such risks. "The protocol developed by Brandt is a paradigm for other late-onset, incurable diseases," says Nancy Wexler, president of the Hereditary Disease Foundation and a leading HD researcher. "It's very responsive to individual needs."

This summer a 44-year-old Baltimore native named Jack was waiting to have the first of at least three pre-test counseling sessions, spaced over a two-month period. Jack had already cleared the neurological exam that, if it had turned up HD symptoms, would have made testing redundant. Though Jack is healthy, he was well versed in the disease: his grandmother and mother died from it, and he knows there is a fifty-fifty chance that he has inherited the time-bomb gene. Two siblings have tested negative, two others positive. One sister is battling symptoms, including a depression that has landed her in a psychiatric ward. "Until now," Jack says, "I haven't cared to know my destiny because I didn't want it to change how I face my day-to-day life."

But Jack's life has undergone some seismic shifts in the past 18 months. His marriage of 12 years collapsed, and he was fired from a job in his wife's family's business, leaving him to search for new career options. "It became evident to me that I didn't have control over my life," he said a few days before the counseling session. "This is one small piece where I can get some control." Jack thought that a negative test result--one that showed no abnormality in the gene IT-15 on chromosome 4--would inspire him to consider moving to another part of the country. And if the news was bad? "Maybe I would be less of a Type A and not work as hard," he said.

Jack had some firm ideas. If the news was good, he would not tell his two siblings who tested positive. "I wouldn't tell them that I'm lucky and reconfirm that they're unlucky," he said. He was so certain that he neither wanted nor needed counseling that he had not yet picked the "confidant" who the program stipulates must accompany him to future sessions. "After what I've been through the last 18 months," he said, "I can handle anything."