A new study finds that the age of both mothers and fathers is a major factor in the risk that a child will develop an autism spectrum disorder.
A major epidemiological study of American children published in the latest issue of the American Journal of Epidemiology has found that older parents, both mothers and fathers, are more likely to have a child with an autism spectrum disorder (ASD).
The study results suggest that mothers aged 35 or older have a 30% greater chance of having an autistic child compared to mothers aged 25 to 29, while fathers older than 40 had a 40% higher risk than those aged 25 to 29.
In addition, the study noted that firstborn children were the most likely to be affected by ASDs; firstborn offspring of 2 older parents being 3 times more likely to develop autism than third or later-born offspring of mothers aged 2034 and fathers aged less than 40.
The study was conducted by Dr Maureen Durkin and colleagues from the University of Wisconsin School of Medicine and Public Health and was funded by the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia.
The researchers looked at data from 10 US study sites participating in the CDC's Autism and Developmental Disabilities Monitoring Network. Out of 253,347 children born at the study sites who had complete parental age information 1,251 were identified as having an autism spectrum disorder at age 8 using the Autism and Developmental Disabilities Monitoring Network. ASDs refer to autistic disorder, pervasive developmental disorder not otherwise specified (PDD-NOS), and Asperger's syndrome. The diagnoses were all made according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision criteria.
With this data in hand the researchers reviewed the parental age information to look for a correlation with ASD incidence to come up with their conclusions. Other factors such as gender, gestational age, birth weight, multiple births, maternal ethnicity, education and site of recruitment were all taken into account. This was done to insure that the age of mothers and fathers could be said with some degree of certainty to be an independent risk factor for the development of ASDs.
The researchers however did note drawbacks to their study design which may have affected the reliability of the results. For example they did not take into account infertility treatments and rates of mental illness or personality traits amongst the parents.
It was also noted that older parents may be more knowledgeable and aware of the signs of developmental disorders and therefore be more likely to seek medical advice and a diagnosis for their child. This could account for at least some of the differences in ASD rates among children of parents in different age groups.
Despite the limitations of the study Dr. Durkin and colleagues conclude that the results provide the "most compelling evidence to date that autistic spectrum disorder risk is linked to both maternal and paternal age, and decreases with birth order.
They also say that the increase in a rise with both maternal and paternal age has potential implications for public health planning and investigations of autism.
The apparent rise in ASDs in the western world has coincided with a trend towards parents having children at an older age, together with a decline in the size of families, so the study results support this potential connection.
The link between autism and the age of parents is currently unclear, but the researchers speculate that the sperm of older men may be more susceptible to uncorrected genetic mutations which are passed on to the child. In older women, age related complications and chromosome alterations are suggested as possibilities.
The study although flawed does provide compelling evidence for a link between the age of both parents and ASDs, but as the researchers themselves admit, large long-term studies of well-characterized birth cohorts are needed to confirm the findings.