Children born to men age 40 and older are more likely to develop autism, according to a new study.
Autism is characterized by social and language abnormalities and repetitive patterns of behavior. Autism and a number of related conditions, known collectively as autism spectrum disorders, have become increasingly common, affecting 50 in every 10,000 children as compared with five in 10,000 two decades ago.
Experts are divided about whether these dramatic numbers are the result of higher levels of awareness and better diagnosis, or whether they represent a real increase in the incidence of autism.
Older parental age has been linked to abnormalities in brain development; however, few previous studies had examined the connection between parental age and autism.
Abraham Reichenberg, Ph.D., of the Mount Sinai School of Medicine, New York, and Institute of Psychiatry, King's College London, and several colleagues evaluated this association using data on children born during the 1980s in Israel. All men and three-fourths of the women born in these years were assessed at age 17, as part of the military draft process, for autism and other psychiatric disorders. Dr. Reichenberg and colleagues obtained draft board information and the age of the father for 318,506 individuals; the ages of both parents were recorded for 132,271 of those.
They found clear evidence that advancing age among fathers is associated with increased risk of autism. After the researchers controlled for year of birth, socioeconomic status and the mother's age, the odds of autism spectrum disorder were nearly six times greater among children of men age 40 and older than those of men 29 years and younger. Older age among mothers was not associated with any increase in autism.
Reporting their findings in the September 2006 issue of Archives of General Psychiatry, the authors discuss possible genetic mechanisms for the paternal age effect, including mutations in sperm-producing cells or age-related problems in genetic "imprinting," which affects gene expression.
"Although further work is necessary to confirm this interpretation, we believe that our study provides the first convincing evidence that advanced paternal age is a risk factor for autism spectrum disorder," they conclude.