Chronic fatigue syndrome; it is a debilitating and puzzling disorder that affects about one million people in the U.S.

CFS strikes women more than men, usually in their 40's and 50's.

But now, this disorder is being recognized as a problem in children too.

15-year old Ellen Nadeau was diagnosed with chronic fatigue syndrome four years ago.

Ellen said, "It is hard to deal with because I have to make sure I get enough sleep and that I don't get sick."

Most commonly seen in middle-aged women, Ellen was initially misdiagnosed.

Ellen added, "I went to numerous doctors and at first I was told I was lactose intolerant."

For the first time, a pediatric definition for CFS is being presented at an international conference in Fort Lauderdale.

It will be published in a journal next month.

Leonard Jason, ph.d. of DePaul University stated, "Some children have things like abdominal pains, rashes, sleep cognitive memory problems so they sometimes have a constellation of problems that are different than the adult population."

CFS in children usually strikes between the ages 10 and 17 and about 80% recover.

That is a much higher percentage than adults.

But one in five will remain debilitated; the causes are unclear.

Leonard Jason said further, "I mean it could be one of a variety of things. We're not sure. We're certainly looking at different types of causes. It could be some type of bacterial or viral infection that a child gets like flu or mono and they basically just don't recover from it."

Differentiating how this disease affects children, like Ellen will make it easier for doctors to make a diagnosis and raise awareness.

Her two siblings also have CFS.

Ellen’s mother Pam said, "We had nightmares with the school district. The social services threatened to remove our children from our home because they thought we were just keeping them home on whim."

Also presented at the chronic fatigue conference, promising evidence that anti-viral therapy may help some patients.