a man and a young childWhat causes autism? Researchers continue to investigate the many factors that can contribute to the development of autism. One such study from Sweden linked a higher risk of autism to the age of the child’s father. Many recent studies have focused on environmental factors that contribute to a risk of autism spectrum disorders (ASD), but relatively few have examined the role of the father.

The researchers examined data from over 2.6 million children born in Sweden between 1973 and 2001. They screened out children who were born prematurely or late and children who immigrated from another country. They controlled for factors like gender, birth order, and the mother’s age.

The results revealed that children born to fathers older than 45 years have a higher risk of developing autism spectrum disorders. Children born to fathers older than 45 were 1.76 times more likely to have autism than children born to fathers 20 to 24 years old. The relationship between autism and paternal age was especially clear when the researchers compared the risk between siblings who shared a father.

Children of older fathers were 13 times more likely to have attention deficit hyperactivity disorder (ADHD) and had double the risk of substance abuse.

Why is it more likely that older fathers will have a child with autism? The researchers suggest that the higher rate of ASD is probably connected with genetic mutations, which accumulate over time, especially in rapidly dividing sperm cells.

This research is published in JAMA Psychiatry.

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