Here's what Dr. Bryan Jepson thought he knew about autism six years ago: that it was a rare, genetic, developmental, untreatable brain disorder. But that's the "old autism," he says.

Jepson, who graduated from the University of Utah School of Medicine in 1995, says what he knew about autism then he mostly learned from the movie "Rain Man." Later, in 2001, his lovable, happy 18-month-old baby began to change — to "fade away," as Jepson puts it. The toddler no longer wanted to be read to, wouldn't look his parents in the eye and liked to spin in circles in the middle of the floor.

A child psychiatrist told Jepson and his wife, Laurie, "Prepare yourself for the time when Aaron will need to be institutionalized. Forget experimental therapies."

Instead, Laurie Jepson took to the Internet. And before long, her husband — who categorizes himself as a "mainstream" physician — was deep in medical literature about the biochemistry of autism. Soon he was convinced that autism is a complex metabolic disease that has as much to do with the gut as it does with the brain.

Bryan Jepson, who is now director of medical services at Thoughtful House Center for Children in Austin, Texas, is back in Utah this week to talk about his new book, "Changing the Course of Autism: A Scientific Approach for Parents and Physicians." On Saturday, he will speak at a free workshop sponsored by Porter's Hope, a Utah-based company that assists the families of children diagnosed with autism.

"All of a sudden, there's an explosion of autistic kids," Jepson says. As recently as 1980, autism was rare, with a rate of about 1 in 5,000. Now, he says, it's 1 in 160.

It's an epidemic, he says, "and there's no such thing as a genetic epidemic."

At the same time, the "new autism" is less likely to show up within the first six months or year of a baby's life, and is much more likely to be "regressive," showing up at 18 months to 3 years to rob the child of previous skills — sometimes almost overnight, sometimes as a gradual decline.

There's a genetic susceptibility for autism. But something else has to explain the sudden rise in numbers — and it's not simply a matter of better diagnosis or a broader definition of what autism means, he says.

The answer appears to have something to do with the increased toxicity of the environment, he says, from food additives to vaccines and antibiotics. Children who are born with a genetic susceptibility for autism have trouble detoxifying, he says.

The increase in other chronic diseases such as asthma is evidence that autistic children may also be proof of what's to come, he says. "It's kind of like the canary in the coal mine."