Once a rare diagnosis, it seems there’s now an epidemic of autism sweeping the nation. Many of us know a child with the disorder, and concerned parents are searching for suspicious signs even in young babies. But while more kids are being labeled with autism, whether the condition is truly more common among today’s children than past generations of youngsters is largely unclear.
There’s no question that autism diagnoses are increasing, but it's unknown how much of that is due to greater awareness of the disorder by doctors and the public, a broader definition of it, a true increase in incidence or other factors.
“There is a chance we’re seeing a true rise, but right now I don’t think anybody can answer that question for sure,” says Dr. Chris Johnson, a professor of pediatrics at the University of Texas Health Sciences Center at San Antonio and co-chair of the American Academy of Pediatrics Autism Expert Panel.
Parents who believe the disorder is increasing due to some modern threat that is damaging the brains of children have pointed the finger at childhood vaccinations and the mercury-containing preservative thimerosal that was once widely used in many of them. There are also suspicions about lead or other toxins in the environment, diet, viruses and medications. Indeed, some experts say it's possible that exposures in utero or in early childhood may play a role.
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Frustrated parents struggling to cope with a disorder that seemed to appear virtually overnight understandably want answers. But clear insights are hard to come by.
Studies done in the 1960s indicated that autism was quite rare, affecting only about one person in every 2,000 to 2,500, according to the Centers for Disease Control and Prevention. Other research in 1970 put the figure at one case per 10,000, Johnson says.
Precisely how many people have autism today is unknown. But estimates suggest there are five to six cases of autism spectrum disorders (ASDs) per 1,000 people, says Johnson. That roughly equates to as many as one case out of every 166 people.
It’s important to note that today’s figures apply to the whole category of ASDs, which includes autism as well as related conditions like Asperger Syndrome and Pervasive Developmental Disorder Not Otherwise Specified. Children with these disorders have varying degrees of impaired communication and social interaction.
Diagnostic criteria changed dramatically in 1987, broadening the number of people who could be considered to have ASDs. In decades earlier, only those with severe autistic characteristics would be diagnosed with autism; others might have been categorized as mentally retarded, for example. So making comparisons across decades is difficult.
“The frequency of the diagnosis has clearly increased but that doesn’t tell you beans,” emphasizes Dr. William Barbaresi, a pediatrician at the Mayo Clinic in Rochester, Minn.
To get a better picture of autism and its potential causes, Barbaresi and colleagues examined new cases of autism in Olmsted County, Minn., from 1976 to 1997.
Using data on every child living in the county during those years, the researchers used modern diagnostic criteria to conclude that the incidence of autism specifically rose dramatically, from 5.5 cases per 100,000 children from 1980 to 1983, to 44.9 cases from 1995 to 1997.
A sharp increase started between 1988 and 1991, a period during which broader diagnostic criteria for autism were newly in use and increased awareness of the disorder occurred, Barbaresi says.
The findings of the study, published in the January issue of the Archives of Pediatrics and Adolescent Medicine, appear to rule out suspects like vaccinations as a cause for the increase, according to Barbaresi.
Other studies also have failed to link vaccinations to autism, prompting the Institute of Medicine, an independent group that advises the federal government, to conclude there is no connection.
But no one knows exactly what causes ASDs, and until they do, much about these disorders will remain a source of great speculation.
To say that there’s a lot doctors don’t know about these conditions is “an understatement,” says Dr. Leonard Rappaport, director of the Developmental Medicine Center at Children’s Hospital Boston.
“Most things we don’t know,” he says.
Rappaport suspects there may be a true rise in ASDs, though he says it’s not at all clear why or to what extent.
To better understand the causes, and hopefully improve diagnosis and treatment, Rappaport is involved in a new study that is focusing on genetic underpinnings of the disorders that he says may play a role in upwards of 90 percent of cases. The federal government also has organized an international coalition to explore the genetics.
Many scientists believe that ASDs are largely caused by genes. Studies have shown, for instance, that if one identical twin has autism the second twin is very likely to also have the disorder. But the risk isn't 100 percent, suggesting that other factors can contribute, even if they aren't the main cause.
“I think it’s clear that there’s a strong genetic predisposition,” says Dr. Steve Sommer, chairman of the department of molecular genetics at City of Hope National Medical Center in Duarte, Calif.
One theory behind a cluster of cases of high-functioning autism and Asperger Syndrome in Silicon Valley holds that people who carry the genes gravitate toward high-tech professions like computer science that don't necessarily require a lot of social interaction. And when these people, who may not have the full-blown disorders, meet and have children together, the kids could be fully affected because of the double genetic whammy from both parents.
Down the line, scientists suspect they may find many genes involved in ASDs.
Sommer’s research has shown that a mutation in the neuroligin 4 gene, which is involved in creating healthy connections between neurons in the brain, is defective in about 3 percent of people with autism. But that doesn’t mean that everyone who inherits the defective gene will develop autism, he says. And there are likely many more genes that play a role in the condition in certain people.
“From a genetic point of view, autism is likely to be many — perhaps a hundred or more — diseases,” he says.
But if autism spectrum disorders are truly on the rise, genes aren’t the reason. “The gene pool doesn’t change,” explains Rappaport. “It would have to be something that’s environmental.”
That something — if it does exist — remains a huge mystery and a source of endless worry for parents, especially given that there is currently no known way to prevent autism.
Rappaport says many parents fear they may have done something to trigger the problem, like taking their kids to get regularly scheduled immunizations or exposing themselves to environmental toxins.
“Parents are searching for answers, and they’re blaming themselves for a million different things,” he says.
“I can’t even imagine all the sleepless nights.”
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