At 22 months old, identical twins John and Sam Fetters couldn't speak a word. By their second birthday, the Gaithersburg boys had both been diagnosed with autism, leaving their parents wondering if they got a double stroke of bad luck, or if genetics could be responsible.
Researchers have known for years that when one identical twin has autism, the other is also likely to be diagnosed with it - evidence that autism likely has a genetic component.
Recent studies support that theory. Researchers at Kennedy Krieger Institute studied 277 pairs of twins and found that when one identical twin had the disorder, the other developed it 88 percent of the time; for fraternal twins, that figure was 31 percent.
In another recent study, an international team led by Johns Hopkins researchers identified a gene that could play a role in developing autism.
Despite this progress in unlocking the mysteries of autism, scientists have simply confirmed that there are likely numerous genetic links to autism. Pinpointing those links and how they work is exceedingly complex and may take years to unravel, let alone counteract.
Each discovery explains just a tiny fraction of autism's causes. Researchers think the great majority - 90 percent - of autism cases have a genetic cause, but they've found fewer than 10 percent of the triggers.
The need for answers is huge. Federal researchers reported last month that nearly 1 percent of 8-year-olds nationwide struggle with the puzzling neurobiological disorder - indicating autism might be more common than previously thought. The causes of autism have bedeviled researchers for years, but the findings are fueling a push among experts to redouble their efforts to hunt for possible genetic and environmental explanations.
When scientists first delved into genetic research on autism, they hoped to find one or two genes to explain the disorder, said Dr. Gary Goldstein, president and chief executive of Kennedy Krieger Institute, which specializes in children's developmental disabilities. Instead, researchers have found about 50 genes so far that might be tied to autism, which explain very few cases, he said.
Autism isn't one disease; it's too individual to locate just one genetic cause. It's not like cystic fibrosis, a disorder for which researchers have identified one gene - and tests to diagnose it.
Instead, autism researchers envision that a wide variety of gene defects are responsible for the symptoms collectively known as autism spectrum disorders. The disabilities, different in each child, range from the mild Asperger syndrome to more severe impairments in social interaction and communication.
"Autism could have 100 different causes," said Jonathan Pevsner, a Kennedy Krieger neuroscientist who is studying a genetic basis for a form of autism in which children have such extreme behavior problems that they injure themselves.
Still, Pevsner is hopeful scientists will make great strides.
"I feel that we should be very hopeful - at the same time realistic - about how difficult it is to untangle all the different causes of autism," he said. With recent breakthroughs in DNA sequencing, researchers can analyze the genomes of people with autism faster and cheaper. "This provides a far more detailed look at possible genetic causes than ever before."
Still, as far as tracking those genes down, scientists are just at the beginning, said Aravinda Chakravarti, a professor of molecular biology and genetics at McKusick-Nathans Institute of Genetic Medicine at Hopkins, who led the Hopkins research.
"It's going to take some work before we understand the true causes of autism," he said. "We need to make much more headway to ever have enough understanding so that patient management and therapies can be improved."
His goal: to understand what's happening with autism on the molecular level and identify causes that can lead to effective treatment that millions of parents so desperately hope for.
Disorders like autism are not only perplexing to scientists, they're frustrating, Chakravarti said.
"We attach much more meaning to them than to other disorders, because they have to do with the basic aspects that make us human - our ability to feel, to think, to speak," he said. "It destroys, often, the sense of self that we have."
The twins study came from findings from Kennedy Krieger's Interactive Autism Network. The project, set up two years ago, has 32,000 participants and is known as the largest worldwide clearinghouse of data from people such as Kim Leaird and Mike Fetters, the parents of identical twins John and Sam. Scientists use that data to investigate genetic and environmental links to autism.