Sean Green was a happy, easygoing baby until one morning, when everything changed.
"He didn't know who I was," his mother, Cyndi Greene, told ABCNEWS correspondent Jackie Judd on World News Tonight. "He looked right through me."
The diagnosis was autism. The brain disorder left Sean lethargic, unresponsive to sounds, disconnected from the world around him.
Dr. Jeff Bradstreet says he sees more and more children like Sean. In fact, he has a waiting list just to get on the waiting list.
"We all feel like we're the captain of a lifeboat of the Titanic trying to decide who can we let in when we're surrounded by people who are more or less drowning with the disease," says Bradstreet.
A decade ago in Loudon County, Va., four autistic children attended public schools. Today, there are 181.
And it costs twice as much money to educate them as other children
"With the rising numbers, the growing needs, the individual needs of students, because students with autism vary so greatly, I think it's going to be quite a challenge," says Charlotte Crane, an autism resource specialist in the county.
The great mystery is why the number of children with this disorder, which affects how different parts of the brain communicate, is rising.
"It presumably affects the developing brain prior to birth," says Wendy Stone, clinical psychologist at Vanderbilt University Medical Center in Nashville, Tenn. "It is generally assumed that there is no single cause of autism in all cases, but that a variety of different causes, alone and in combination, contribute to the development of autism in different individuals."
Nancy Minshew, director of the Collaborative Program of Excellence in Autism at the University of Pittsburgh, says the environment may play a part.
"It's a polygenetic disorder, which means each case is caused by three to four interacting genes, but you can't have a genetic epidemic. So the increase would have to be a genetic-environmental interaction. I don't think anybody had a clue, which is scary," she says.
Another controversial theory points to vaccines as a possible cause of autism. But experts say there is no scientific evidence to support this.
"There have been studies looking at the MMR vaccine and the relationship of that to autism," says Lisa Freund, a developmental neuro-psychologist at the National Institutes of Health in Bethesda, Md. "But they haven't produced any solid evidence of a connection. Many show absolutely no relationship at all."
She says this theory has scared a lot of parents, but strongly discourages them from steering away from vaccines.
"Until we have some evidence that there is a strong relationship between the two, it can't be recommended to not have vaccines. Not having them could be disastrous," she says.
Mercury, which has been known to cause neurological defects, particularly if exposure occurs in utero, is at the center of another controversial theory.
Some parents feared that the mercury in vaccines might cause autism, but scientists say there is actually very little or no mercury in vaccines these days.
"Vaccines have not had mercury in them for years," says Freund. "And if that had a direct impact, we would probably have seen a decrease in a reporting of the disorder, and that has not occurred. However, it would be important to know the symptoms of children who did receive this and have the disorder. It could be that some children, because of a genetic predisposition, have a vulnerability to low doses of mercury, which results in something along the autism spectrum."
Researchers at the Centers for Disease Control in Atlanta are now planning to conduct research revolving around mercury.
Dr. Pauline A. Filipek, director of the Departments of Pediatrics & Neurology at the University of California-Irvine College of Medicine, says if mercury were the culprit, statistics would have pointed to the association earlier.
"There would be a much higher prevalence in countries that consume fish [which can have a higher mercury content] as a major staple to their diet, like Japan," she says, but notes "the prevalence is the same there as it is in the U.S."
There is also disagreement about how best to help autistic children
Some parents use a variety of treatments. More than half try alternative methods such as special diets, nutritional supplements, even medications to remove mercury from a child's body.
Cyndi Green and her husband, John, tried a variety of treatments for their son, but taking Sean off milk helped the most.
"The result was nothing short of spectacular. Within two to three days Sean started to actually speak again, which we hadn't heard in a long time," says John Greene.
Minshew advises parents to approach alternative treatments with caution.
"There's always a miracle story like that going around," she says. "The problem is that we have a disorder where we have some treatments that are effective, but not in all children and not to the extent that we want them to be."
She adds: "It is important to keep in mind that there is no cure. Parents have to put their foot down, because they're so vulnerable, and say, 'Give me some proof before I put my heart on the line and put my child through this.' These children don't like change."
Experts agree that mainstream treatments, which involve behavior modification to learn gestures and words, are the most effective.
"The best treatments are educational and behavioral. Children with autism require specialized interventions because of their unique learning and behavioral characteristics. The use of different forms of Applied Behavior Analysis is generally considered best practice," says Stone.
Jadie Vigil's three autistic children went through this process. "The difference after the therapy is amazing, really amazing. It completely turned [around] my children's lives, I feel, completely," she says.
One drug has also shown promise. A study in a recent issue of the New England Journal of Medicine focused on Risperidone, a drug shown to improve disruptive behaviors associated with autism.
"These disruptive behaviors not only interfere with the acquisition of adaptive skills but are very distressing to families and therapists," says Deborah Fein, professor of psychology at the University of Connecticut in Storrs.
But Fein admits the drug's potential is otherwise limited. "It is disappointing, but not surprising, that the medication had no effect on the more central symptoms of autism that were measured, namely social withdrawal and noncommunicative use of speech."
However, eliminating some symptoms could pave the way for different drugs to treat other symptoms. "If irritability, hyperactivity, and stereotypes were reduced by use of Risperidone, the child's core autistic symptoms and deficits might be more amenable to other treatments, such as behavioral treatments, over the long term," says Fein.
Minshew believes that in this day and age, with all of the scientific advancements being made, hope for a cure is at an all-time high.
"With the decoding of the human genome, there will be a cure for children born today with autism," she says. "Progress is moving at a visible pace. So our goal right now is to get what we do know and implement it into practice."