What causes autism? While the condition is not new, doctors and scientists are unsure of its exact causes. Scientists say genes may play a role, although no single gene or genes have been discovered to definitively cause autism so far. Others blame the child's pre- and postnatal environment. "Today" host Matt Lauer reports.
Three-year-old Xavier Trent has autism. He and his entire family — mother Kimberly, father Mark and brother Jordan — are at the Vanderbilt Kennedy Center in Tennessee to give samples of their blood. They are involved in a study of DNA that will hopefully give scientists clues to unlock the secrets of autism.
“There may be a gene or a series of genes that may cause autism,” said Kim Trent.
In fact, experts say five to twenty genes may be responsible for causing autism.
“I think it's very clear genes are involved in making you prone to autism, maybe even causing autism,” said Dr. Gary Goldstein, a child neurologist who directs the Kennedy Krieger Institute in Maryland. “What we don't know is just how many and which ones.”
Discovering the genes for autism could lead to earlier diagnosis, intervention and perhaps drugs to treat the disorder. But with the reported increase in cases of autism, some believe something else in addition to genes may be causing the condition.
“There's really the role for something in the environment that could be triggering someone who is genetically susceptible,” said Goldstein.
“I think there's a real concern that there's been a change in our environment,” said Dr. Carol Berkowitz, president of the American Academy of Pediatrics. “An exposure to some toxins, chemicals, environmental factors — either when a mother is pregnant or after the delivery of the child — that has led to autism.”
Possible exposures include pesticides, flame retardants and even pre- and postnatal viruses.
One possible factor still remains controversial. Though health officials insist that childhood vaccines are safe, some believe that exposure to the mercury preservative once found in most childhood vaccines can cause autism.
“He was not developing and he became worse and worse,” said Lynne Avram, who thinks the mercury preservative, thimerosal, may have caused her son, Paul, to develop autism.
More from TODAY.com
Hillary Clinton: Granddaughter led me 'to speed up' political plans
Clinton said she is inspired to keep working to ensure that Charlotte and her generation are provided equal opportunities ...
- Lauren Hill, inspirational college basketball player, dies
- Marathon dad's victories help raise money for son with spina bifida
- Will it work on Vale? Savannah tries tissue sleeping trick at home
- Listen to the chilling 911 call Sandra Bullock made during break-in
- Hillary Clinton: Granddaughter led me 'to speed up' political plans
“I think the trigger for him was the cumulative mercury burden from his vaccines, because his body was not able to get rid of the mercury like you and me.”
Dr. Kenneth Bock believes that autism can be effectively treated through special diets, nutritional supplements and removal of toxins. Bock tested Paul's urine and found elevated mercury levels.
“He had elevated levels of not only mercury but cadmium, lead, arsenic and tin,” said Bock. “There may be a subset of children that are more susceptible to mercury and therefore react this way in terms of the autism spectrum.”
Bock detoxified Paul's body of heavy metals through chelation therapy. He used an FDA approved medicine, called DMSA, which has been used for decades to treat lead poisoning. It has the potential for side effects like liver problems, but Bock says the drug has a good safety profile.
“Two years after he started treatment, he would look at me and say, ‘Momma, I love you,’ ” said Avram, who lives in Cheshire, Conn.
Bock also treated Paul with glutathione, a protein that detoxifies the body of heavy metals.
But the Institute of Medicine, which looked at the link between autism and childhood vaccines, has found no "causal relationship."
“My response to the parent who's truly convinced and can't be swayed is that there's not much that you can say to them, other than the evidence does not support their point of view. But even trying to remove mercury does not improve the outcomes of these children,” said Dr. Marie McCormick of the Harvard School of Public Health.
The Institute of Medicine also found no published clinical studies showing that chelation works.
“The use of chelation in children with autism is a totally unproven therapy,” said McCormick. “And chelation is not a procedure without side effects in some individuals.”
The CDC says that childhood vaccines are, and have always been, safe.
“Right now, the scientific evidence doesn't provide any framework for concluding that thimerosal or immunizations in any way affect autism,” said Julie Gerberding, director of the CDC. “But we have to have an open mind about that.”
Others point out that if the mercury in vaccines was the culprit, the rate of autism would have started to decline after 1999. That year, health authorities urged manufacturers to remove thimerosal from all childhood vaccines except the flu shot — in order to make sure parents would vaccinate their children.
“If indeed, the thimerosal, which is no longer there, was provoking this epidemic of diagnosis of autism, then we ought to see a marked decrease in the number of children we diagnosed with autism. To date that is not happening,” said Goldstein.
Journalist David Kirby is the author of a new book, "Evidence of Harm," which examines whether the mercury in the preservative of vaccines can cause autism.
“I think there is a body of evidence that actually dovetails quite nicely into a workable, plausible theory,” said Kirby. “That still is far from proof. We need to get to the bottom of this.”
Others say autism may be caused by the body's response to a particular injury or inflammation.
“There may be an immunologic component, like we've seen in people who have arthritis and other inflammatory diseases. And I think that mechanism could well be something worth exploring in what's going on in autism,” said Goldstein.
Still others say it might be diet. Barbara Guterman believes the tuna fish she ate while pregnant caused both of her sons, Blake and Brett, to develop autism.
“I ate a can of tuna fish every single day, thinking I was eating a healthy protein source,” said Guterman.
In fact, health officials recommend that pregnant and nursing women consume no more than 12 ounces of fish per week. Experts also warn pregnant women against extreme dieting.
Given all these possibilities and no answers, most agree more studies are needed.
“We need more people, more scientists in every area, to be aware of autism, and if the funding were there we would find many, many more scientists working in this,” said Goldstein. “Do we need it? Absolutely, because we don't have the answer.”
© 2013 MSNBC Interactive. Reprints