NewYork-Presbyterian. The University Hospital of Columbia and Cornell.

--The risk of developing autism is significantly higher among children born to men who are 40 and older than it is among children with fathers under 30, scientists report in the Archives of General Psychiatry.

Autism is a growing problem, affecting 50 children in every 10,000, compared with just five in 10,000 only 20 years ago.

This ten-fold increase appears to be partially due to more awareness of the condition and a broader definition that includes autism spectrum disorders. However, it could also be that there is an increase in the actual incidence of autism, experts say.

According to the Autism Society of America (ASA), autism is a complex developmental disorder that affects social interaction and communication. Individuals may be affected differently by the disease. The term Pervasive Development Disorder (PDD) is used by professionals to cover the spectrum of autistic disorders, which include Asperger's and Rett's Disorders. Childhood Disintegrative Disorder is another condition that falls under the PDD umbrella, according to ASA.

Aging May Affect Genes

There may be several genetic reasons for this finding, says study author Abraham Reichenberg, Ph.D., from Mount Sinai School of Medicine, in New York City.

One cause might be mutations in the sperm as men age, Dr. Reichenberg says. "Those mutations might be accumulating with age and therefore transmitted from the father to the child," he says. "Another possibility is that mechanisms that the body has to protect itself from mutations are not working that well with age."

It might also be that an improper or defective gene is being activated, Dr. Reichenberg notes. These mechanisms operating alone or in concert may be the reason for the association of older parental age and autism, he says.

Mother's Age Not Strongly Linked to Autism

In their study, Dr. Reichenberg's team collected data on the age of the fathers of 318,506 people born during the 1980s in Israel. The age of the mother was known for 132,271 of these people as well. Among these individuals, all of the men and three-fourths of the women were assessed by the draft board at age 17 for any psychiatric disorders.

Among those whose father's age was the only one known, 208 children had a diagnosis of autism spectrum disorder, as did 110 in the group where the age of both parents was known, the researchers found.

When the researchers compared the parents' age when they had their child to the cases of autism among the children, they found:

• 34 cases among 60,654 kids born to parents aged 15 to 29 years old
• 62 cases among 67,211 kids born to parents aged 30 to 39 years old,
• 13 cases among 4,106 kids born to parents aged 40 to 49 years old
• and one case among 190 kids born to parents older than 50.

Findings Spark Further Questions

Dr. Reichenberg's group found the advancing age of fathers was associated with increased risk of autism. In fact, the odds of a child having autism spectrum disorder were nearly six times greater for children of men aged 40 and older, compared with men aged 29 years and younger. The older age of mothers was not associated with the risk for autism.

"This phenomenon of older fathers having autistic kids should be explored further, because it might give us a clue about the genetic mechanism that contributes to the development of autism," Dr. Reichenberg says.

One expert thinks the finding might be explained by the fathers being mildly autistic, and therefore marrying and having children later.

"The very real possibility that autistic traits in fathers led to older age of marriage and age at childbirth presents a real problem for interpretation of the results," says George M. Anderson, Ph.D., a research scientist at the Child Study Center and Laboratory Medicine at the Yale University School of Medicine. "This critical aspect is downplayed by the authors."

"In the absence of good sociability/integration data in fathers of autistic children, I think one can say little about how much of the reported paternal age effect in autism is due to age-related genetic alterations," Dr. Anderson says.

Always consult your child's physician for more information.