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Thursday, September 7th, 2006
The Age of Autism: About those 'old dads'
WASHINGTON, Sept. 6 (UPI) -- The study released this week that found older fathers more likely to have autistic children has created a media stir. But there may be less to the story than meets the eye.
"Autism Risk Rises With Age Of Father -- Large Study Finds Strong Correlation" was the headline on the top left of the Washington Post's front page.
It's nice to see autism on the front page and, yes, the study drew from a large pool, "an enormous sample of 17-year-olds" in Israel over a period of six years in the 1980s, as the Post put it. The researchers were able to determine the age of both parents for 132,271 draft candidates.
And yes, older men were found to have a greater risk of fathering an autistic child than men under 30.
Yes, but: The study was done in another country, involving kids born 20 years ago when the autism rate was much lower. Plus, there's something called the "confidence interval" -- basically, the margin of error -- in scientific studies, and it comes into play here. In a letter to Britain's Daily Mail, researcher Clifford Miller wrote:
"There were only 13 autistic children born to fathers 40 and over considered in the study -- there were 128,000 children with fathers under 40 but only 4,000 with fathers over 40."
Given that not-so-enormous number in the key demographic, the margin of error in calculating the increased risk is ... well, enormous.
"The lowest risk figure of 2.65 times for fathers 40 and over fathering an autistic child is exactly the same as the highest risk figure for fathers between 30 and 39."
Those overlapping figures "could be used to argue that there is no significant difference between dads in their 30s and 40s," said Mark Blaxill, a vice president of the advocacy group SafeMinds, which believes that an environmental factor -- possibly the mercury in vaccinations -- is behind the huge rise in U.S. cases over the past 20 years.
Still, Blaxill calls the result "interesting" -- "All data is good, in my view, and this is data." He notes that previous studies of parental age and autism risk have had mixed findings. "If it's a factor, it's certainly not an overwhelmingly large one."
The most important issue is what the study appears to suggest: "Autism Study Hints at Genetics," as the Wall Street Journal's story put it. The idea is that spontaneous mutations in the dad's genes would, as time goes on, raise the risk of autism-inducing errors.
Yes, but: Even assuming larger, more current studies in the United States exactly replicated these findings, why would they hint at genes more than an environmental cause? The longer someone lives, the likelier they are to get all kinds of exposures that could affect their DNA. (Or, older parents could differ in some other way that would raise their child's risk of autism.)
This column recently has been highlighting a "chemical connection" that early researchers turned up, a link that was all but abandoned in favor of gene theories.
One such study was conducted by Dr. Mary Coleman, who described a key finding in the 1976 book The Autistic Syndromes.
"In the preconception history questionnaire filled out by both the father and the mother, there were two areas of marked difference between the parents of the autistic children and the parents of the controls. One of these areas was exposure to chemicals," Coleman wrote. (The other was hypothyroidism.)
Note -- she was looking at "preconception" history, which could suggest some kind of genetic damage from chemical exposure that was passed on to the children in the form of autism. The age of the fathers was not recorded, but wouldn't they get more such exposures as they got older -- making the "chemical connection" even stronger? For career chemists, as some were, that is almost a given.
"Clearly, this is an area where more prospective research is needed," Coleman wrote. It still is.
We've also pointed out a possible connection in the very first cases described in the medical literature -- 11 children born in the 1930s -- with new chemical compounds, plausibly including mercury-based fungicides. One of those 11 kids was the son of a plant pathologist, another the son of a forestry professor at a southern university, and a third grew up in an area being heavily planted with seedlings to create a national forest in Mississippi (there's that southern forestry connection again -- in fact, his home town is named Forest).
A fourth was the son of a mining engineer. And the very first case to come to medical attention, at Johns Hopkins University in 1935, was the son of a 30-year-old chemist-attorney at the U.S. Patent Office. A chemist.
Yet the tendency to see just about everything as powerful support for the "gene theory" is proving just about irresistible -- even when the evidence at hand amounts to 13 children born to older fathers in Israel in the 1980s.
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