INDEPENDENCE TOWNSHIP -- The rates of autism in children have risen 700 percent nationally and more than 1,500 percent in Michigan since 1992, according to a recent study, and no one in the medical industry or government knows why.

But Gary and Rose Lannen may have come up with their own solution to the mystery.

Two years ago, their son, Sean, then 3, could not speak. He growled at strangers. He wouldn't let his parents or anyone else touch him.

He was eventually diagnosed with pervasive developmental disorder, a milder form of autism.

Now, Sean, 5, talks and acts like any normal kindergartner as he greets a stranger who knocks on his front door.

"These are my brothers, Robert, Thomas and David," said Sean, making the introductions of the other boys in his Independence Township home. "But there are no girls here."

His parents won't go so far as to say that Sean has been cured of autism, a neurological disorder that some authorities say has reached epidemic proportions in recent years.

"We like to say he's on the road to recovery," Rose Lannen said.

While Sean Lannen's experience is not unheard of, it is unusual, said Dr. Catherine Lord, a professor of psychology and psychiatry and director of the Unviersity of Michigan's Autism and Communication Disorders Center.

The autism center has about 200 autistic children from across the country under long-term study. Sean Lannen is not part of the study.

"We probably have 10 kids in that group whose parents would say, 'Look, they don't have autism anymore.' But when I see them, I see remnants of autism," Lord said.

Rebecca Landa, a speech-language pathologist and autism expert at the Kennedy Krieger Center of Johns Hopkins University in Baltimore, cautioned that parents of other autistic children should not get their hopes up.

"I've had a couple of cases (like Sean's), but only a very small minority of these children (can appear normal)," she said. "People are seeking a cure. But there isn't one."

The Lannens say Sean is making progress toward recovery because they put him on a gluten- and dairy-free diet and enrolled him in an intensive, behavior-therapy program recommended by, among others, the Autism Research Institute of San Diego.

The institute's director and father of an autistic son, research psychologist Bernard Rimland, admits much of his program is not accepted by mainstream doctors.

"Only a small fraction of autistic kids recover because only a small fraction of parents follow this procedure," Rimland said. "Traditional doctors will tell you that's nonsense, but that's because they're ignorant."

As recently as the early 1990s, only about one in every 2,500 children was diagnosed as autistic. Some researchers are suggesting the current rate is as high as one in 150.

The apparent explosion in autism cases has produced speculation over a possible environmental cause. Some parents have blamed vaccines, despite a Danish study that said the vaccines given to young children appear to be safe.

Other experts say the definition of autism, which was first described in the 1940s, has been medically broadened to include many related conditions. Also, public schools are being required to offer more services to autistic children.

An often-referenced California study showed the number of children diagnosed with autism in that state more than tripled from 1987-1998. A follow-up study released last year showed the numbers continuing to climb.

An Internet newsletter on autism, The Schafer Report, quotes U.S. Department of Education data that show the number of Michigan children diagnosed by their public schools as autistic has risen from 12,222 in 1992 to 97,847, an increase of 701 percent.

Public schools in Wayne, Oakland and Macomb counties say the number of children enrolled in their autistic programs has more than doubled since 1996.

Gary and Rose Lannen say Sean was developing normally as a toddler. His behavior changed after he received a series of common children immunizations about age 2.

"You couldn't get near him," Gary Lannen recalls. "If strangers came into the house, he would hide. He wouldn't play with his toys, but he would walk around all day with the same toy."

The first few doctors who examined Sean gave his parents no satisfactory answers.

One doctor told the couple that Sean would be fine if they waited another six months.

But the Lannens took a proactive approach. They read books on autism, conducted research on the Internet and contacted the Oakland County chapter of the Autism Society of America.

One of the first changes they made was to remove dairy and gluten-containing foods -- wheat, oats, barley and rye -- from Sean's diet.

"There was an amazing change in Sean's behavior after only a couple of weeks on the new diet," Rose Lannen recalled.

However, autism experts Lord and Landa say there is no scientific evidence that nutritional changes have any effect on autistic symptoms.

The Lannens also enrolled Sean in the fall 2000 in the newly opened Early Interaction Center in Birmingham.

Jennifer Wiessner, the local center's executive director, said Sean Lannen was one of the first three autistic children accepted by the center -- and its first graduate.

"When Sean first came into our clinic, he had no verbal language, but he growled," Wiessner recalled. She described the kind of progress that he has made since then as "pretty rare."

"You have to catch it early enough, and you have to have the treatment intensive enough, and you have to do it the right way," Wiessner said.

Sixteen children are now enrolled in the Birmingham clinic.

Therapy costs the center about $6,000 per month, per child. Scholarships and fund-raisers bring the cost for each family down to $4,000 a month.

Sean Lannen was a 30-hours-a-week patient of the clinic for several months, and then was a part-time patient from February 2001 until last September. His parents estimate the treatment there cost them about $50,000. Savings and generous relatives paid the bills.

Now, Sean attends a regular kindergarten class at his neighborhood elementary school. But his parents say he has a long road ahead.

You can reach Mike Wowk at (586) 468-0343 or mwowk@ detnews.com.