New scientific research reveals that frequent genetic mutations in the U.S. population can cause autism, a neuro-developmental brain disorder that affects one in every 150 American children. But many researchers say the groundbreaking study is only one piece in the puzzle to determine the cause of autism.
Autism is a lifelong condition that encompasses a range of disorders known as Autism Spectrum Disorders that affect children in early infancy. Autistic children often have difficulty socializing and communicating with others and, in some cases, are incapable of performing basic functions.
Autism was first diagnosed in 1943, but many scientists say it remains a mystery partly because of the complexities of the brain. But a recent study at New York's Cold Spring Harbor Laboratory points to a possible genetic cause, as geneticist and lead author Jonathan Sebat explains.
"The study, led by Mike Wigler and myself, has found that in at least ten percent of sporadic cases of autism, the primary genetic factor involved is a spontaneous mutation. It was not something that the mother or the father was carrying. One interesting thing about our findings is that the mutations occur at many locations throughout the genome [i.e., all of the genetic information that an individual possesses]," says Sebat. "And what this seems to suggest is that autism does not arise from changes in a single gene or even a handful of genes, that there are 50 or possibly 100 different sites in the genome that, when altered, can contribute to autism."
Finding an Elusive Cause
Most scientists agree that there is a genetic basis for autism. But an increase in autism reported by the U.S. Centers for Disease Control this year has prompted scientists to look elsewhere for possible causes. According to the report, one in every 150 U.S. children is autistic, compared to between two and six per one-thousand in the past decade. Neurologist Mirjana Savatic of New York's Stony Brook University says the increase may be partially due to improved diagnostic technologies.
"New assessment tests have been developed that we can use to better diagnose children with autism. So in the past, somebody who was diagnosed with mental retardation is now diagnosed more properly as an Autism Spectrum Disorder [case]. However, there is no decline in the diagnosis of mental retardation throughout the United States. So there is also a true increase in the number of cases of autism that we see," says Savatic.
Whatever the reason for the increase, no one really knows what causes autism, says Ami Klin, a professor of child psychology and psychiatry and Director of Yale University's Autism Program.
"We know that autism is not a single condition. There is tremendous variability - - individuals with profound mental retardation, individuals who are very gifted intellectually, individuals who don't speak at all, individuals who speak too much," says Klin. "Right now, what we know is that probably the most significant contribution comes from genetics. But it's clearly the case that it's not only genetic. And there are likely other factors involved. What they are, we don't know quite as yet."
The search for the causes of autism also includes environmental factors such as exposure to lead and mercury, and preservatives in children's vaccines. Epidemiologist Irva Hertz Piccioto at the University of California at Davis is researching environmental contributors to autism.
"Lead toxicity in young children causes things like mental retardation and some organic pollutants like P.C.B.s [i.e., polychlorinated biphenyls, which are industrial chemical compounds] can affect cognitive development in young children. And we are looking at pesticides or chemicals that are in home products. And we're also interested in microbiological factors like viruses and bacteria. And the reason for that is that is one of the few factors that we know can be related to the development of autism," says Piccioto.
Asking the Right Questions
Most experts agree that there is no evidence to link autism to any one cause. And because autism encompasses a wide range of disorders and affects people very differently, many analysts expect its causes to be as different as the children it affects. Indiana University's Cathy Pratt is the Director of the Indiana Resource Center for Autism and board chairperson of the Autism Society of America, the nation's largest grassroots autism movement.
"Some families will say that from the moment their child was born, they noticed that there was something different. Other families, their child develops skills and then at a certain age, all of a sudden they [lose those] skills. What there is probably some common consensus about is that there is a genetic predisposition for autism," says Pratt. "But then where a lot of the work is being focused on now is if we have that genetic predisposition, then what could be the trigger?"
That may be the wrong question, some analysts say, because autism could be a symptom of other ailments. In order to uncover what causes autism, Eli Hatchwell, Director of the Genetics Core Facility at Stony Brook University, says a major shift in the way people perceive autism is needed because no single cause will ever be found.
"In the future there will be many, many hundreds of different specific causes that will be related to the development of autism, including environmental and including possibly vaccines," says Hatchwell. "But it would be more a case of this gene causing maybe half-a-percent of autism, this gene maybe causes two percent, this environmental factor maybe causes one percent. So it's going to be a ragbag of different things. And we have really only just scratched the surface as far as doing these studies."
There is no cure for autism, although each of its various symptoms can be treated through therapy and medication. But researchers at the Cold Spring Harbor Laboratory hope that by identifying mutant genes and malfunctioning parts of the brain, better ways can be found to treat autism.
This story was first broadcast on the English news program,VOA News Now. For other Focus reports click here.
