The number of school-aged children with an autism disorder in the United States may be significantly higher than previously thought, according to a new report published online Wednesday by the Centers for Disease Control and Prevention (CDC).
Data analyzed for the report suggests that in 2011-2012 as many as 1 in 50 U.S. children between the ages of 6 and 17 had been diagnosed with autism, Asperger’s syndrome or a related developmental disorder, up from 1 in 86 in 2007.
The authors of the report note that autism diagnoses rose among all age groups, and particularly among teens aged 14 to 17, one of several factors that suggest that most of the increase in prevalence was the result of previously undiagnosed cases.
Also on Wednesday, a team of European and Australian researchers published a study online in JAMA Psychiatry that found that men who father children at older ages have an increased risk of having a grandchild with autism.
Based on parent surveys
The CDC’s new findings are based on more than 95,000 parent telephone surveys taken between February 2011 and June 2012. Parents were asked if a doctor or other health-care provider had ever told them their child had autism and if their child currently had autism. These answers were then compared to a similar survey taken in 2007.
In the more recent survey, 2 percent of the parents (1 in 50) reported that they had a school-age child with diagnosed autism compared to 1.6 percent (1 in 86) in 2007.
Much of the increase involved older children who had been diagnosed with autism since the last survey. These children also tended to have milder symptoms. Such factors suggest, according to the CDC researchers, that the increase is not due to more children having autism but to a greater awareness by parents and clinicians about the disorder and its symptoms.
The survey also found that boys were four times more likely to be diagnosed with an autism disorder than girls. Other research has suggested that boys are more likely to have genetic variants that make them more susceptible to the disorder.
This survey has its limitations, of course. Most notably, only 23 percent of the parents contacted agreed to answer the survey’s questions. That’s down from 47 percent in 2007. Differences between people who responded to the survey and those who didn’t may have biased the results.
Last year, another government report found that 1 in 88 U.S. children had an autism disorder. That report looked at the medical and educational records of 8-year-olds in 14 different regions of the country.
For the JAMA Psychiatry study, researchers used data from Swedish national registries to identify 5,936 people with autism and 30,923 without the disorder who had been born after 1932. The registries provided other data for each of these individuals’ families, including the age at which their grandfathers had fathered their parents.
An analysis of the data found that men who fathered a daughter at the age of 50 or older were 79 percent more likely to have a grandchild with autism than men who had a daughter between the ages of 20 and 24. Among older men who fathered a son, the increased relative risk for having a grandchild with autism was 67 percent.
The researchers controlled for a variety of factors, including age of spouse, family history of psychiatric disorders and level of education.
It’s important to point out that this was an observational study, which can show only a correlation not a cause-and-effect between two things. The absolute (as opposed to the relative) risk for any individual family would be quite small.
Father’s age also a factor
Other research has reported an association between older fathers and an increased risk of autism among their children. One study published in 2011 found that fathers aged 50 and older were 2.2 times more likely to have a child diagnosed with autism than those under age 30.
“This study goes beyond that and suggests that older grandpaternal age is also a risk factor for autism, suggesting that risk factors for autism can build up through generations,” said the lead author Emma Frans of Swedens’ Karolinska Institutet in a prepared statement.
Frans and her colleagues note that the mechanism behind this increased risk is unknown, but it may be explained by age-related genetic mutations and alterations in male sperm cells.
But, again, the absolute risk to any particular family is small. “Older men should not be discouraged to have children based on these findings,” write Frans and her co-authors, “but the results may be important in understanding the mechanisms behind childhood autism and other psychological and neurodevelopmental disorders.”
The CDC report can be downloaded and read in full online. The JAMA Psychiatry study is, unfortunately, behind a paywall.