Autism Spectrum Disorder: Prevalence and a New Risk Factor

Summary and Comment |
April 12, 2013

Autism Spectrum Disorder: Prevalence and a New Risk Factor

  1. Barbara Geller, MD

The increase in prevalence seems to have occurred in one epidemiologic group; older grandfathers, like older fathers, seem to increase the risk.

  1. Barbara Geller, MD

Two recent articles provide updates on epidemiology and paternal age risk in autism spectrum disorder (ASD).

To examine childhood ASD prevalence over time, researchers examined CDC telephone interviews with parents in 2007 and 2011–2012 (63,967 and 65,556 offspring aged 6–17 years, respectively). Parent-reported prevalence increased from 1/86 to 1/50, largely due to increases in boys and teens aged 14 to 17, who were more likely to be diagnosed with mild ASD. ASD prevalence remained similar in the population that was included in both surveys (this cohort included 56,399 children aged 2–13 years in 2007), thus ruling out methodological errors accounting for the increased prevalence.

Older paternal age is a risk factor for ASD, but the impact of grandparent's age has been unknown. To learn more, researchers used data from Swedish birth and psychiatric registries to examine age of parents and grandparents when the child and the father were born. Parents' ages were available for at least 90% of both cases and controls and grandparents' ages for at least 60%. There were 5936 ASD cases born after 1932 and 30,923 unaffected controls with complete data. ASD risk increased monotonically for both father's and grandfather's ages. Maternal and paternal grandfather's age over 40 was associated with a 3% attributable risk (AR; i.e., cases that would have been avoided if the grandfather had been younger) and father's age over 40 with a 6% AR.


As prevalence of autism spectrum disorder rises, physicians need to address pregnancy risks that are amenable to interventions, such as adequate folate intake, flu vaccination, nonpharmacological treatments attempted before antidepressants, and alternatives to valproate. The data do not yet support advising men to freeze their sperm while young, but other data support the concept that freezing sperm and using in vitro fertilization are not in themselves likely to worsen fetal outcomes. But which mutations cause ASD by themselves or when added to other risks is not yet ascertainable.


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