Autism Awareness
    Autism: Does Increased Parental Age Mean Increased Risk?
    By Kimberly Crandell | April 26th 2010 12:26 PM | 6 comments | Print | E-mail | Track Comments
    About Kimberly

    I'm a mother of three, with an aeronautical engineering degree.  Although it's been a while since I've done any aircraft


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    The possibility that autism is more common in offspring of older parents has generated considerable interest. To investigate the theory, a study using data from 10 US study sites participating in the Centers for Disease Control and Prevention's Autism and Developmental Disabilities Monitoring Network, was developed to examine the relation between parental age at delivery and the prevalence of autism spectrum disorder (ASD). Confirmation of such an association has important public health implications in light of increasing trends in recent decades for couples to delay having children.

    The study used data from 253,347 study-site births with complete parental age information. Cases included 1,251 children aged 8 years with complete parental age information from the same birth cohort and identified as having an autism spectrum disorder. In evaluating the association between parental age and autism risk, it was important to account for other variables related to both parental age and. Birth order is a potentially confounding factor because it is positively associated with parental age and has been reported in some studies to be associated with autism risk, with at least 3 studies reporting firstborn children to be at increased risk of autism. The goal of this study was to determine, in a large, population-based cohort of US children, whether advancing maternal and paternal age each independently increase a child's risk of developing autism after controlling for the other parent's age, birth order, and other risk factors.

    In unadjusted analyses, both mean maternal age and mean paternal age were significantly higher for ASD cases than for the birth cohort as a whole. With parental age 25–29 years as the reference group, the odds of developing ASD was significantly reduced for parental age <20 years and increased for maternal age 35 and paternal age 40 years. Those age cutoffs (maternal age 35, paternal age 40 years) were used to classify each parent's age as "older" versus "younger." Other significant predictors of ASD in unadjusted analyses included low birth order, male gender, advanced maternal education, and preterm birth.

    Multivariable analysis of parental ages modeled as categorical variables
    After the data was adjusted for the other parent's age and other covariates, the increases in ASD risk associated with maternal age 35 years and paternal age 40 years (relative to age 25–29 years) were slightly reduced compared with the unadjusted analysis. In contrast, the results for birth order suggest that the decline in ASD risk associated with increasing birth order is somewhat stronger in the adjusted analysis than in the unadjusted analysis. In addition, the apparent increase in ASD risk associated with higher levels of maternal education in the unadjusted analysis is no longer evident in the adjusted model, suggesting that the apparent maternal education effect is due to its association with parental age.

    Parental ages modeled as continuous variables
    In unadjusted analyses, the risk of developing ASD increased significantly with each 10-year increase in both maternal age and paternal age. After adjustment for age of the other parent and other covariates, each 10-year increase in maternal age was associated with a 20% increase in ASD risk while each 10-year increase in paternal age was associated with a 30% increase in ASD risk.

    Combined effects of parental age and birth order
    The risk of ASD within each of 3 parental age categories (both parents "younger," 1 parent "older," and both parents "older") was highest among firstborn children and declined with increasing birth order . Considering the combined effects of parental age and birth order, (excluding from the analysis births to mothers aged <20 years), the lowest risk group to be third- or later-born offspring of mothers aged 20–34 years and fathers aged <40 years. The risk of ASD increased with both declining birth order and increasing number of older parents. The highest risk group included firstborn offspring of mothers aged 35 years and fathers aged 40 years, with a risk 3 times that of the reference group.

    The overall results of this study provide the most compelling evidence to date that ASD risk increases with both maternal and paternal age and decreases with birth order.

    Source: American Journal of Epidemiology, Advanced Parental Age and the Risk of Autism Spectrum Disorder

    If you're interested in reading additional articles on autism, ScientificBlogging's Autism Awareness page provides a listing of all the articles on our site that touch on the subject.


    Larry Arnold
    Maybe, that is all I can say, but on Saturday it was my immense pleasure to attend the wedding of two autistic friends of mine, the bride already pregnant. What are here chances of bearing an autistic child, notwithstanding more severe than the pair of them?

    Who knows, but do any of us, what is coming next week or next year, or tomorrow?

    Autism may be an obvious here and now hit, but do any of us know what the future for so called neuro typical and able bodied people is? how much of perhaps debility in the last quarter of ones life is, and how would one react to such risk?

    It is all relative.

    Is ASD a risk? No I say, life is a risk. The perfect child can be run over after a glittering University career on the cusp of graduation. So what is real?
    Kimberly Crandell
    Good point, Laurence.  "Risk" is a loaded word, and isn't necessarily the best term to use.  It should probably just be stated as an increased occurrence.  

    The facts of this study appear to be that a larger percentage of children born from older parents (moms over 35, dads over 40) are diagnosed with ASD, as compared to the percentage of children that are born from "younger" parents that receive the same diagnosis.  If that diagnosis is viewed as a "risk", that really is an individual perspective - and there are probably as many opinions on that as there are families touched by autism.
    Larry Arnold
    I'm not disputing the studies, in my family there has been a tendency to marry late in some cases, and who knows sometimes where sociology and genetics interact, whether there is something perhaps in families bearing what has come to be called the "broader autistic phenotype" some other social factor that predisposes one to marry and bear children later. The phenotype equips one with a certain set of social traits and those social traits in turn will perhaps determine genetic ones and the direction of the relationship will be equivocal.
    Larry Arnold
    I realise I have commited a faux pas there which needs explaining.

    When I say social traits will determine genetic ones, I essentially mean that social patterns may determine what Simon Baron Cohen has called selective mating, and indeed if there is a higher risk of autism in older parents, any social propensity to start a family later in life, will lead to that higher risk of spontaneous genetic mutation that could lead to autism.
    I see there is a correlation of older parents and autism. It is more in the mother than in the father. For older fathers, I would think that they are less play outdoor with their children. When children don't have enough natural stimulation from the environment, their brain can be imbalaced easily, then we see autistic symptoms. For older mothers, their sudden hormonal changes can affect the fetus significantly. For example, when the mother has insulin resistance during pregnancy she can cause many unwanted chemicals to enter the fetus. These unwanted chemicals can cause inflammation in the brain. Autism Spectrum Disorder is popular in high tech and fast food countries. It will be very difficult to find an autistic kid in Vietnam 30 years ago. ASD is an disorder when parents spent very title time with the child. The children brains need to interact directly from real human from very early ages. Frog leaps, TV, and/or video games will do more damages than good for young brains (even adult brains). I have treated many autistic children and was able to help them to say good bye to autism. My treatment was based on brain balance and food/chemical sensitivties elimination. You don't have to look for gene therapy...because there isn't any. Cheers.

    Why would ASD rates be higher in firstborns than in later children? That seems counter-intuitive to the age theory. And also, perhaps I can let out my breath for good now on my third child, the only one who--so far--seems to be NT.