And though they were told that their children could have inherited the mutant gene, they had no idea what had been unleashed into the family.

Dr. John Roberts, the neurologist who now treats John, remembers thinking once that John Askew, a man who loved his children more than his own life, had planted land mines in his family.

They were about to explode.

· · · · ·

John and Lael called a family meeting with Amy, her husband Robert and Danny. They were waiting for genetic confirmation but felt they had some answers to John's problems. And it was clear that the children could be affected.

"They told us that John might have a disease called Huntington's and that there was a 50 percent chance the children could have inherited it," Robert Bishop, Amy's husband, remembers.

It was February 1995, and by this time Scott Askew was an attorney in Phoenix, Amy was expecting her fifth child, Charlie was working for Sprint in Kansas City and Jane, the psychologist, was beginning to raise a family in Florida. Danny was the only one living at home.

Julie's life was more complicated. She was still recovering from the brain damage she suffered in the car wreck five years before. They all recognized that she would never be the same.

When her parents told her about Huntington's, she said, "I hope I don't have it. I have enough problems already."

· · · · ·

Gene testing for Huntington's has only been possible since 1993, though a less-accurate method was developed in 1983, using a genetic marker that had been located near the fourth chromosome. That process involved tracing the marker using DNA samples from not only the subject but close relatives. It was a long and complicated process that was only 95 percent accurate.

A neuropsychologist named Nancy Wexler had used her private fortune to fund the research that found the marker. Her mother had the disease. At that point, only time would tell her whether she would have it, too.

They located the Huntington's mutation in 1993 when researchers figured out the critical area is in a set of three DNA bases or "tri-nucleotides," C, A and G. The number of times those bases are repeated is associated with the chance of developing Huntington's disease.