Feb. 9, 2012 at 9:34 AM ET
By Rebecca Ruiz, msnbc.com
Drew and Skyler Russert are 16-year-old identical twin brothers from Los Altos, Calif. who share the same blue eyes, straight hair and love for football.
Looking at them now, on the football field or in their high school classes, it would be hard to tell the boys were diagnosed with autism when they were nearly 4. Drew had a moderate form of the disorder, while Skyler’s case was severe.
Their parents, Peter Russert and Gaynelle Grover, were surprised by the diagnosis. The Russerts had no family history of autism, but they suspected a combination of environmental factors and genetics as a possible cause.
Was it local pollution or perhaps a viral infection during Gaynelle's second trimester? Was it their ages? Gaynelle was 40 and Peter was 44 when the boys were born.
"There is this horrible emotional feeling, like this didn’t have to happen,” Gaynelle says.
While genes or genetic mutations were once thought to account for up to 90 percent of the risk for developing the brain disorder, recent research increasingly points to environmental triggers.
Previous research on twins found very high rates of autism among identical but not fraternal twins, indicating that the disorder was predominantly a genetic one.
However, a Stanford University study of 192 twins with autism -- including Drew and Skyler Russert -- found notably higher rates in fraternal twins, who do not share identical DNA. The research, which was published last summer in the Archives of General Psychiatry, suggests environmental factors -- such as parental age, low birth weight and maternal infections during pregnancy-- could account for 55 percent of a person’s susceptibility to autism.
Other recent studies have demonstrated an increased risk among mothers who don’t take prenatal vitamins, those who live within 1,000 feet of a freeway or who used a certain type of antidepressant in the first trimester.
A new study published in the American Journal of Human Genetics gave some clues as to how this might happen. In particular, genes linked to autism are more actively regulated during the transition from fetal to post-natal development, making them especially sensitive to environmental influence. This period of changes, during which genes can be turned on or off, might be critical for developmental brain disorders, according to the researchers.
Dr. Thomas Lehner, chief of genomics at the National Institute of Mental Health, says the Stanford study makes a compelling case that environment is an important factor. “[Genes] still play a role,” he says, but the “interplay between gene and environment could be very important to figure out.”
The Russerts embraced a combination of traditional and nutritional therapies in attempts to alleviate the boys’ symptoms and improve their language and communications skills. Like many parents of autistic children, the Russerts tried a complex combination of dietary changes, like gluten-free meals and enzyme and vitamin supplements to eliminate perceived environmental threats.
"It’s a little bizarre ... as a parent to turn into a scientist,” says Peter.
Alycia Halladay, director of research for environmental sciences for the New York-based advocacy organization Autism Speaks, says the best parents can do is have as healthy a pregnancy as possible and, if a child is diagnosed, consult a physician about any autism-related treatments. Even though the vaccine-autism theory has been debunked, Halladay says it remains a compelling explanation to some parents -- often to the exclusion of risks for which there is scientific evidence.
“There’s a huge group of people that when you say environmental factors, they limit that to vaccines,” says Halladay. “They don’t think about all of the other things that could play a role.”
Instead, Halladay says parents might focus more on minimizing stress and exposure to toxic chemicals, as both have linked to changes in the brain that might affect the way genes are turned on and off.
Autism Speaks, which helped to fund the Stanford study on twins, has backed efforts to identify environmental factors, such as nutrition and toxins, that could be linked to autism. The organization has also supported Early Autism Risk Longitudinal Investigation, or EARLI, a study that is collecting environmental samples from the homes of parents with one autistic child and a newborn.
It will be years before EARLI is finished. Meanwhile, research continues to provide some clues to autism. A recent small study in the Archives of General Psychiatry linked environment to the regulation of certain genes susceptible to autism, although they did not identify specific environmental triggers.
The Russerts say Drew and Skyler aren’t consumed by discovering the origins of their autism. After years of speech and occupational therapy, the boys feel like they have overcome the disorder. They are both on track to attend college, and the communication difficulties and repetitive behaviors they experienced as toddlers are mostly gone.
Peter and Gaynelle are grateful for the outcome, but don’t claim to know exactly what helped the boys move beyond their original diagnosis.
“We’d all love that one little miracle puzzle piece,” says Gaynelle, but until the science is clear, “I don’t know we’ll have one answer for every kid.”
Rebecca Ruiz is a senior editor at msnbc.com and a Rosaylnn Carter Mental Health Journalism Fellow
Copyright 2013 Thomson Reuters.