A group of autism researchers at the University of California Davis conducted a massive records-based study analyzing "all the singleton births in California during the 1990s for which information was available about the ages of both parents, a total of about 4.9 million births and 12,159 cases of autism."
The findings suggest that mothers giving birth over the age of 40 are significantly more likely to have a child with autism. Meanwhile, according to an article in the LA Times, "For men over 40, there was a 59% increased risk of autism if the mother was younger than 30, but virtually no increased risk if the mother was over 30."
These findings may appear to be a smoking gun - a straightforward explanation of the rise in autism spectrum diagnoses. But in fact they would explain the incidence of only about 5% of the rise in diagnoses over the past ten years:
The number of women over age 40 in California giving birth increased by 300% in the 1990s, while the diagnosis of autism increased by 600%. At first glance, it might seem that the rise in older pregnancies could be responsible for the rise in autism, which is now thought to affect as many as one child in every 100. But the authors, from UC Davis, calculate that older mothers account for less than 5% of the increase in autism diagnoses.
Here's a quick glance at the paper's abstract:
Based on the first examination of heterogeneity in parental age effects, it appears that women's risk for delivering a child who develops autism increases throughout their reproductive years whereas father's age confers increased risk for autism when mothers are <30, but has little effect when mothers are past age 30. We also calculated that the recent trend towards delayed childbearing contributed approximately a 4.6% increase in autism diagnoses in California over the decade.
While the facts discovered are intriguing, they don't seem to add a great deal to our understanding of the roots of autism. In fact, says one senior researcher, we have a long way to go in understanding the roots of autism. In fact, Dr. Hertz-Picciotto adds:
...older women may be followed more closely during pregnancy, which would mean more ultrasounds -- which a few researchers have suggested might play a role in autism. Older women are more likely to suffer gestational diabetes and to develop autoimmune disorders, both of which have been linked to an increased risk of autism.
This new study seems to only bring about more questions and concerns. I feel deeply for the families dealing with autistic children and trying to help them live normal lives. We can only hope that these ongoing research studies begin to uncover more valuable clues to a cure.
Thanks for the post.
Hi Lisa,
Isn’t it funny how reality works?
Have a real phenomena–like parental age influencing autism risk–and when to test for the risk you find it.
Rather striking contrast with false risks–which you don’t find when you test for them.
Interesting…reality is.
W&N
Trouble with the “age of parents” studies is that no one seems to know what the actual link might be. Is it genetic (age of egg/sperm)? Is it related to environmental toxins? Is it about ultrasounds, gestational diabetes, or…??
Or could it be that older parents are more likely to be starting a family late because of social/communications delays that they themselves experienced?
In short, while an association has been found, I’m not sure how useful the finding really is.
Lisa
…or it could be related to the idea that older parents are more likely to be more affluent and educated. It reminds me of the California ‘hot spots’ they found…in areas with wealtier school districts. I don’t have studies to prove it, but I would suspect that professional moms are more likely to wait on having kids until they are more ’settled’. With economic factors having a fairly significant influence on autism ‘rates’, I’d like to see them dealve into that aspect…
re: Lisa’s comment #3 – Those are good points.
W&N, haven’t I often heard you say not to confuse correlation with causation?
I have always wondered if my age had something to do with both my boys having autism. I had my first son at age 37 and second one at 39, not exactly over 40 but close.
But it’s interesting that the study suggests women older than age 40 because I know at least two moms who had kids at age 40 and 41 (boy, girl) and they are neurotypical kids.
There must be some correlation with age though because at the special day preschool where my youngest attends, the other moms with autistic children had their children when they were in their late 30’s like myself.
My husband is a year younger than me so I can’t blame him.
Thanks for the article Lisa!
Regarding Lisa’s question in comment #3 “Is it related to environmental toxins?” see this U.S. News & World Report article about a UCLA study on mercury (which was published in the journal Biometals:
http://www.usnews.com/health/family-health/womens-health/articles/2009/08/24/blood-mercury-levels-rising-among-us-women.html
The number crunching Laks did off of that data had NOTHING to do with autism prevelence; instead it just documents the increased levels of mercury. You make the assumption that there is statistical relationship between autism rates and mercury exposure. I could probably come up with a dozen other 10 X more likely ’suspects’ for increased rates of autism in older women; the aforementioned socio-economic factors being one of them. Of course, we can’t say that increased buildup of toxins in older women are not a major factor in ALL of the increased risks of everything from miscarriages to chromosomal abnormalities; but taking a mercury/causation position is grossly oversimplifying a much more complex and broad toxic environment issue that the world faces…
Looking at mercury causation as an important factor is not an oversimplification. If there are many factors, many toxins etc., that is no reason to not look at any of the factors individually.
Speaking merely as a layperson who reads, I believe mercury can cause autism. That doesn’t mean it’s the only cause of autism.
http://www.autism.com/triggers/vaccine/mercury.htm