Parental Age and Autism

Recent studies have shed light on the increased risk of autism based on parental age.  While for some time the risks for children’s health and older mother’s has been emphasized (including lower birth weight, higher risk of birth defects and chromosomal conditions such as Down’s Syndrome), only recently has paternal age also been identified as a risk factor.  On the maternal side, researchers at the University of California, Davis conducted a ten year study in the 1990’s, examining 4.9 million births.  The older mother’s age at conception was associated with increased risk of having a child with full syndrome autism.  Other studies examining this issue include a 2007 Kaiser Permanente study indicating increased risk for autism with both maternal and paternal older age at time of conception, and an Israeli study from the 1980’s noted paternal age as linked with greater autism risk

The recent UC Davis study, with a greater sample size, found that mothers over the age of 40 had 51 percent higher odds of having children with autism compared with mothers between the ages 25 and 29.  The father's age also played a factor, but only when he had a child with a woman under 30.  While autism rates have risen 600 percent in the past two decades, older women having children contributed to only 5 percent more cases of autism.

The latest research by the Icelandic firm Decode Genetics, published in the journal Nature last month, indicates that older men are more likely than young ones to father a child who develops autism or schizophrenia, because of random mutations that become more numerous with advancing paternal age.  This study is also the first to quantify the effect as it builds each year. The age of mothers had no bearing on the risk for these disorders, with the research finding that although maternal age may be paramount for chromosomal abnormalities, the majority of genetic risk for complex developmental and psychiatric problems originates in the sperm.  The overall risk offspring of a man in his 40s or older is in the range of 2 percent, at most, and there are other contributing biological factors that are entirely unknown.  The risk is higher by age 35 and continues to creep up with age.  While the increasing age of parents at the time of conception contributes to the significant increase in autism, it is still not enough to explain for the extremely high rate of autism, the fasted growing developmental disorder, now affecting roughly 1 in every 100 American children.

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