Dad's age not related to autism

Studies that have suggested that older men are more likely to father autistic children have seriously overstated the risk, concludes a large new analysis of parental age and autism risk.

Some studies have found an increased risk of autism in children born to older fathers, but others have not. The reported risk varies widely, with one study finding children born to fathers over 40 years at six-fold greater risk of autism compared to those with younger fathers.

To better understand the relationship, researchers looked at the records for all children born in California between 1992 and 2000, nearly 5 million in total. There were 18,731 children who had been diagnosed with autism.

Over the course of the study, the average age of both mothers and fathers rose, while the percentage of moms and dads over 40 years also increased.

According to the data, both mothers and fathers over 40 years had an increased risk of having a child with autism, but the risk varied by birth year. For older mothers, it ranged from a 1.27-fold increased risk for kids born in 1995, to a 1.84-fold greater risk for children born in 1993. Among men, increased risk ranged from 1.29 for kids born in 1992, to 1.71 to for those born in 1995.

The researchers attributed the variation in risk to the fact that the population of people with autism has changed over the years, as more and more children are diagnosed with the disease. For example, 40.3 percent of children with autism born in 1992 were mentally retarded, compared to 22.7 percent of autistic children born in 2000.

The researchers noted that one problem with teasing out the effects of maternal versus paternal age is that older women tend to marry older men, and vice-versa. To account for this, the researchers analysed paternal age and autism risk independently of maternal age.

When they did this, the risk associated with being an older father disappeared. However, when the researchers looked at the influence of mothers' age independently of paternal age, the risk remained. Even then, however, the increased risk of having an autistic child for mothers over 40 years was small, at around 3 percent to 4 percent.

So, the findings indicate that father's age is not a big player in child's autism risk.