Dozens of different gene defects are linked to autism, according to two major new studies of the developmental disorder led by University of California, San Francisco, scientists and involving more than 50 laboratories worldwide.
The mutations — which may work alone or in combination — are all connected by their roles in a few basic molecular pathways, which could be targets for future treatments, according to the two studies, published Wednesday in the journal Nature.
"The genes that we identify are critically important clues about the underlying biology of autism, which we really need to understand to know what is going wrong," said Dr. Matthew W. State, UCSF professor of psychiatry, a co-leader of one study and a key participant in the second.
Not all cases of autism have a gene-based beginning. Growing brains can also be influenced by environmental events.
In many cases, a combination of factors may be involved, he said.
While a rare few of the newly detected mutations are inherited from the parents' genomes, most families do not have a family history of the disorder.
Rather, these mutations arose during the creation of a father's sperm cell or mother's egg cell, they found.
The scientists tied mutations in more than 100 genes to autism. Sixty of these genes met a "high-confidence" threshold, indicating that there is a greater than 90 percent chance that mutations in those genes contribute to autism risk.
The finding that autism can result from mutations in so many genes suggests that it is not a single condition, but rather an umbrella term for patients with similar sets of conditions.
But this doesn't mean that many different treatments will be necessary, State said. Rather, the mutations "coalesce about a much smaller set of biological processes," he said.
The genes implicated in the new studies play three major roles:
- The formation and function of synapses, the sites of nerve-cell communication in the brain
- Regulation of instructions relayed to hundreds, if not thousands, of other genes
- Packaging of DNA into a cellular structure known as chromatin
The researchers studied DNA data collected by the Simons Foundation Autism Research Initiative, a database of families that have one child with autism and unaffected parents and siblings.
"They did great work," said Samuel S.H. Wang, associate professor of molecular biology at Princeton University, who studies the neurobiology of learning with the Princeton Neuroscience Institute.
"What they are doing is finding clues as to which brain pathways go off track to cause autism," said Wang, who was not involved in the research. "This is really about the general biology of what causes autism, not the diagnosis of individuals.
"If enough of these genes are found, it should be possible to start figuring out which molecular pathways — and even which brain systems — go off track in early life to cause autism," Wang said.
- No big smiles or other warm, joyful expressions by six months or older
- No back-and-forth sharing of sounds, smiles or other facial expressions by nine months or older
- No babbling or back-and-forth gestures, such as pointing, showing, reaching or waving, by 1 year
- No words by 16 months
- No two-word meaningful phrases by 2 years
- Loss of speech or babbling or social skills at any age
For more information, go www.autismspeaks.org.
Source: First Signs, a national nonprofit that educates parents on autism
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