This is a guest post from Elizabeth Fernandez of the San Francisco Chronicle. Fernandez is among the first class of AHCJ-CDC Health Journalism Fellows who are spending the week studying public health issues at two Atlanta campuses of the Centers for Disease Control and Prevention.

Amid a seeming explosion nationally in rates of autism, advances are emerging in science’s understanding of the illness, but no cause has yet been found to explain the profoundly puzzling disorder, a government researcher said Thursday in Atlanta.

Multiple causes — a combination of complex genetic and environmental interactions — are likely responsible, said Catherine Rice, Ph.D., of the Centers for Disease Control and Prevention’s National Center for Birth Defects and Developmental Disabilities.

Vaccines have become the focus of concern in recent years among some parents as a possible trigger, but studies generally have found no connection between the two, Rice said.

“There is a strong genetic component, but genes don’t explain everything,” she said.

Autism Spectrum Disorder is the term for a variety of developmental disorders including autism, atypical autism, Asperger’s disorder, and Rett Syndrome — Rett alone has a biologic confirming test.

An estimated 560,000 youths in the U.S. have the disorder. It’s far more prevalent among boys: three to seven boys are affected with the illness for every girl with autism.

“Our best estimate is 1 in 150 or 6-7 per 1,000 children have autism,” Rice said.

Despite a hike in rates over the past quarter-century, attributed to better assessment tools and to a broadening of the diagnostic category, researchers are “more concerned that children are being under-identified than over-identified,” Rice said. She expects a “leveling off” in rates over the next 12 years.

The disorder typically begins to unfold during the first two years of life, often noticed through a lack of interest in interacting with family. The child may engage in repetitious play behavior, may not respond to the parents’ voice “but would respond to, say, the opening of the refrigerator,” Rice said.

By age three, the disorder becomes much more evident. The median age of formal diagnosis is between 4½ and 5½.

Some children with autism have a wide range of impairments; they may have ADHD or self-injurious behaviors. Some children become overwhelmed by sounds, sights, smells. They may suffer from gastrointestinal problems, food sensitivities and sleeping disorders. Preoccupied within their “own world,” some children lack a sense of safety, and may wander into streets or other hazards.

“Children can have a lot of frustration because of their difficulty communicating,” Rice said. “It’s a lifelong disorder. We consider autism an urgent public health concern.”

Pia Christensen (@AHCJ_Pia) is the managing editor/online services for AHCJ. She manages the content and development of healthjournalism.org, coordinates AHCJ's social media efforts and edits and manages production of association guides, programs and newsletters.