John Dailey never knew why he was always so disorganized. His struggles in school grew into struggles at work. But when his 3-year-old daughter started to show signs of attention deficit/hyperactivity disorder, he realized that he had been seeing those very signs in himself his whole life.
"I had given up trying to figure out why I was the way I was and just accepted it and said this is me," Dailey told "Good Morning America."
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Dailey, from Ramsey, Minnesota, was diagnosed with ADHD six years ago, on the same day his daughter was diagnosed. He was 36 years old.
Dailey is among the estimated nearly 5 percent of American adults living with ADHD, according to the National Institute of Mental Health.
Ashley McDermott is another parent whose diagnosis came about because of a child. While she was researching her son's ADHD, she was astonished to find that she was reading about herself.
"I closed the book the second chapter, and started to cry. This is my whole life. I can't believe this is me," she said.
"It was life-defining because suddenly my whole life makes sense," McDermott said. "Every part of my personality that I never could understand why I was the way I was, it all made sense."
Dr. Ned Hallowell, a psychiatrist who works out of Boston and New York, said there was no doubt that ADHD was genetically transmitted.
"There's some cases you can acquire it, but 95 percent of cases you acquire from the genes of your parents and grandparents," he said.
There appear to be differences in the way that grown women and men experience ADHD.
According to Sue Hallowell, Ned Hallowell's wife and author of "Married to Distraction," women are generally "more of the day-dreamy, inattentive type, so they're not the ones who were jumping off the walls like the boys with ADHD with hyperactivity disorder."
McDermott's lack of focus hobbled her in school and followed into her adult life.
"Every single report card -- I mean my entire childhood said the same thing, which is 'Ashley could be a very good student if she could calm down and stop talking and pay attention and focus,'" she recalled.
Dailey had similar obstacles.
"I'd always hit walls in terms of trying to climb the ladder and move onto bigger and better things and a lot of it was because I couldn't get organized," he said.
A combination of medication and behavioral therapies has transformed Dailey. He is now very productive at work and his performance is being rewarded.
"I think the first year on the medication we blew our numbers out of the water and I got about 145 percent bonus, it was absolutely enormous, we'd never seen that much money in one big fell swoop," he said.
Ashley, 45, is about to publish a novel. It's a feat that would have been unimaginable before she started taking medication for her ADD, another clinical term that can be applied to many types of ADHD.
"My ADD literally got so bad that I couldn't even read a book. So you have that constant noise in the back of your head and then suddenly you take your ADD medicine and it's like someone turns the staticky radio off," she said.
Dailey has weaned himself off the medication, but he has new strategies to cope with his disorder.
"If I know I've got a deadline, I'm actually going to shut myself away from everybody and focus in a nice quiet room, typically from my home office as opposed to going into the office, because in the office I'm talking to people," he said.
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