Older moms and dads might be a reason for more autism.
Durkin MS, J Maenner, CJ Newschaffer, LC Lee, CM Cunniff, JL Daniels, RS Kirby, L Leavitt, L Miller, W Zahorodny and LA Schieve. 2008. Advanced parental age and the risk of autism spectrum disorder. American Journal of Epidemology doi:10.1093/aje/kwn250.
Accumulated environmental pollutants in the body and the damage caused by them are offered as possible explanations for the increased risk. One potential cause is chemicals that damage cell DNA, including those pollutants that the parents were exposed to when they were developing in the womb.
Trends in delayed childbirth, which go along with higher education level, and overall greater awareness of autism are explanations that could not be ruled out by the study.
Researchers found a 20% increased risk of autism with each 10-year increase in parents’ age after 25 years. The highest risk was seen in fathers over 40 years (40%) and in mothers over 35 years (30%), compared to 25-29 years.
The risk was also highest for firstborn children and went down with birth order. Fourth born children were half as likely to have autism.
The prevalence of autism in the US is 1 in 150 live births, or less than 1% of births. The rates of the neurological condition have been climbing, and some experts say it is becoming epidemic. Researchers have looked at many factors but have not identified a single cause for the brain dysfunction.
This study used 50% more cases of autism than previous studies. They drew from approximately 325,000 US births. The number of cases and large sample size raises confidence that age and age-related factors are possible causes.
The next challenge is to figure out biologically what is happening. Is it normal aging or something that goes hand in hand with age, such as higher chemical body burdens?