A sweeping study of hundreds of families with autism has found that spontaneous mutations can occur in a parent’s sperm or egg cells that increase a child’s risk for autism, and fathers are four times more likely than mothers to pass these mutations on to their children, researchers said on Wednesday.
The trick will be identifying specific networks in the brain in which these genes interact, so that researchers can begin to develop new treatments.
“We now have a good sense of the large number of genes involved in autism,” Buxbaum said.
One of the studies by Dr. Evan Eichler and colleagues at the University of Washington in Seattle suggested how environmental factors might influence genetics.
They looked specifically to see where these spontaneously occurring genetic mistakes were coming from: the father’s sperm or the mother’s egg cells.
They found that new mutations occurred four times more frequently in sperm cells than in egg cells, and the older the father, the more likely he was to have sperm with these spontaneous mutations.
One possible reason for this, Buxbaum said, is that men make sperm every day, and this high turnover rate increases the chance for errors to occur in the genetic code that could be passed on to their offspring.
“It tells us that sperm production is an imperfect process,” Buxbaum said in a telephone interview.
“It’s primarily driven by a dad’s age. That makes sense. As you get older, there are more and more chances for problems.”
He said these findings support other studies that show older fathers have a slightly increased risk of having a child with an autism spectrum disorder.
Buxbaum stressed that everyone has these slight mistakes in their genetic code, but when they occur in areas critical to brain development, they can cause different types of autism.
Kevin Mitchell, a geneticist at Trinity College Dublin, who was not involved in the research, said in a statement 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.
The researchers say the studies just scratch the surface of what will be needed to fully understand the genetic causes of autism. But the new approach, sequencing genetic changes in the region where genes code for proteins, appears to be the best place to look.
“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.”