Parental age -- especially that of fathers -- plays a key role in whether their offspring are at risk for autism, say scientists who've uncovered new mutations linked to the condition.
Although the DNA mutations, discovered by three teams, are considered relatively rare, the discoveries are helping lay the groundwork for a sharper understanding of autism's genetics. The newly uncovered mutations account for about 15 percent to 20 percent of all cases of autism.
"All of the studies showed that being an older parent was significant," said Dr. Joseph Buxbaum, director of the Seaver Autism Center at Mount Sinai School of Medicine in Manhattan, whose research led to the discovery of one of the mutations.
"But when you drilled down into the data it was the dad, and that finding is consistent with the epidemiological data," Buxbaum said of statistical studies that have also linked older fathers to autism in their offspring.
Mutations were most likely to occur in stretches of DNA on the gender-determining chromosome. Parents older than 35 at the time of their child's conception were most likely to transmit a DNA flaw, each of the studies showed.
In addition to Mount Sinai, gene-mutation discoveries also involved researchers at Yale University and the University of Washington. The studies are reported in the online edition of the journal Nature.
Buxbaum and the other two teams attributed the problem to so-called "de novo gene mutations." These genetic miscues are not passed from one generation to the next but occur spontaneously around the time of conception and are caused by DNA glitches in sperm or egg cells.
Dr. Matthew State, who led Yale's team, said advances in gene-searching technology helped investigators home in on suspect DNA. "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," State said.
The newly identified mutations bring to about 100 the number of known genetic flaws linked to autism spectrum disorders.
"We now have a good sense of the large number of genes involved in autism," added Buxbaum, who estimates that 10 percent of all autism-related genes have now been found.
"In all three papers there are a couple of messages we all agree on," Buxbaum said. "There are a number of genes involved in autism -- about 800 to 1,000.
"That's a big number. But it also puts a boundary on our search and tells us how far we have yet to go," he said.
Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at Cohen Children's Medical Center in New Hyde Park, said scientists have only scratched the surface regarding the complex causes of autism.
"This research does represent yet another genetic advance in terms of understanding the basis of autism in a subset of children," Adesman said. "Unfortunately, we are still unable to pinpoint a specific cause in a majority of children."
The discoveries come on the heels of a federal report last week that revealed autism's prevalence has jumped 23 percent since 2009. The Centers for Disease Control and Prevention now estimates one in 88 children is affected by an autism spectrum disorder.
"We need to study many more parents and their affected children if we are to uncover the genes important in autism spectrum disorders," Buxbaum said, adding that finding additional genetic miscue will lead to earlier diagnosis and possibly even novel drug therapies.