In three independent studies published April 4 in Nature, scientists examined children suffering from sporadic autism, meaning the disorder does not run in their families. The results showed that mutations in the parts of genes that code for proteins influenced on the development of autism.
In the first study took part 677 people from 209 families, each with one child with autism. The study found 126 de novo mutations – coming from neither parent – that were predicted to contribute to autism.
“These results confirm that it’s not the size of the genetic anomaly that confers risk, but its location,” said Dr. Thomas Insel, director of the National Institute of Mental Health, one of the National Institutes of Health, which funded one of the studies.
As the CBS News reports, the experts also found out that these mutations occurred four times more frequently in sperm than in egg cells. And the older the father, the more likely his sperm was to contain these mutations.
The results of the second study, conducted by Yale University researchers, showed that 14 percent of individuals with autism had genetic mutations at a rate of five times the normal rate. And, 39 percent of these mutations were found to affect a key pathway for communications in the brain.
The third study, led by Harvard Medical School and MIT’s Broad Institute, examined rates of de novo mutations in autism spectrum disorders. The researchers found that chance mutations play a modest role in the development of autism, providing small but important evidence of autism risk factors in those mutations.
“We now have a path forward to capture a great part of the genetic variability in autism – even to the point of being able to predict how many mutations in coding regions of a gene would be needed to account for illness,” Dr. Thomas Lehner, chief of the NIMH Genomics Research Branch, said in a news release.
“These studies begin to tell a more comprehensive story about the molecular underpinnings of autism that integrates previously disparate pieces of evidence.”
Kevin Mitchell, a geneticist at Trinity College Dublin, who was not involved in the research, explained the studies help explain how autism can be an inherited disorder but not always run in families.
“The explanation is that many cases are caused by new mutations – ones that arise in the germline (eggs and sperm). The studies reported in Nature are trying to find those mutations and see which genes are affected,” he said.
As Reuters writes, the researchers predict the studies just scratch the surface of what will be needed to fully understand the genetic causes of autism.
“Prior to the advent of new DNA sequencing technology, we were largely wandering in the dark searching for autism genes,” said Matthew State, co-director of the Yale Program on Neurogenetics and a senior author of one the three papers.
“Now we are getting a clear view of the genetic landscape and finally have the tools in hand to find a large proportion of the many genes contributing to autism.”