Autism risk rises with dads’ age

Children born to fathers of advancing age are at significantly higher risk of developing autism compared with children born to younger fathers, according a comprehensive study published Monday that offers surprising new insight into this disorder of the brain.

The finding comes at a time of great controversy over autism in the United States; a recent surge in diagnoses has fueled speculations about various possible causes of the disorder. For scientists, both the origins and potential treatment for the disorder remain a mystery.

With every decade of advancing age starting with men in their teens and 20s, the new study found, older fathers pose a growing risk to their children when it comes to autism – unhappy evidence that the medical risks associated with late parenthood are not just the province of older mothers, as much previous research has suggested.

Of special concern is the finding that the risk for autism not only increases with paternal age, but appears to accelerate.

When fathers are in their 30s, children have about one and a half times the risk of developing autism as children of fathers in their teens and 20s. Compared with the offspring of the youngest fathers, children of fathers in their 40s have more than five times the risk of developing autism, and children of fathers in their 50s have more than nine times the risk.

Autism is a developmental disorder that is often characterized by social and verbal problems. It manifests early in childhood and is associated with learning deficits and other problems. Many cases are diagnosed shortly after children enter school, where differences among kids become obvious.

Several types of interventions are increasingly available for autistic children, but there is no cure for the disorder, and scientists are not sure about its biological roots.

The new study suggests an intriguing new avenue for research because it suggests that genetic traits passed along by fathers, as opposed to mothers, may play some significant role in creating susceptibility to autism. Several other studies have suggested older parents of both sexes are at greater risk of having children with developmental disorders. Three earlier studies looking at the relationship between paternal age and autism have produced mixed results; the new study is the most rigorous analysis conducted to date.

The study was based on a sample of 17-year-olds – nearly all the men and three-quarters of the women of that age found over a six year period in Israel, as they came of draft age. In all, data from 378,891 men and women were analyzed.

Researchers were able to determine the age of both parents for 132,271 draft candidates. They compared that information against medical evaluations conducted by the draft board for autism and other disorders for those candidates.

Abraham Reichenberg at the Mount Sinai School of Medicine in New York along with several others at research institutions in the United States and Israel found a significant relationship between paternal age and autism, even after accounting for other factors such as mothers’ age and socioeconomic status.

In a paper published Monday in the Archives of General Psychiatry, the researchers said that the number of cases of autism among families with the oldest dads was too small to lead to definitive conclusions about that group, but there was little doubt about the overall trend. The only question, they said, is whether the risk accumulates at an accelerating rate with advancing paternal age, as the numbers in this study suggest.

Scientists in the United States are increasingly thinking about autism in terms of a spectrum of problems, which is why they have coined the term autism spectrum disorders. The federal government estimates that the risk for autism spectrum disorders in the United States is about 3.4 for every 1,000 children between the ages of 3 and 10.

Whether that number is on the rise or not has been hotly contested; better outreach and diagnostic efforts may be finding children who would previously have gone undetected. Enduring disparities in access to healthcare complicates the picture. While the medical complexities of autism are present in Israel, concern over disparities is mitigated to some extent because Israel has universal health insurance which guarantees equal access to care.

The Israeli military draft board’s medical diagnostic system does not differentiate among conditions on the autism spectrum, which includes everything from autism to Asperger’s syndrome, Rett syndrome and what are known as pervasive developmental disorders.

Autistic people can be unresponsive in social situations, or focused intently on a single task or object for long periods. In recent years, concern has grown – despite a lack of conclusive evidence – that mercury in children’s vaccines leads to autism.

While the link between older fathers and autistic children is likely to be genetic, the researchers who conducted the new study also acknowledged the possibility that other unknown factors could simultaneously be causing men to delay parenthood while independently increasing autism rates.