Older Parents Are More Likely to Have Children with Autism

Older parents, especially older fathers, are more likely than other parents to have children with autism. This finding, which has been replicated in several large studies, establishes an association between age and autism.

There is no clear indication, however, that parental age actually causes autism. Research is ongoing as to why and how parental age impacts the risk of autism. This article will discuss the evidence as to whether parental age is a risk factor for autism.

Evidence of a Link Between Parental Age and Autism

In 2006, a major study conducted by Abraham Reichenberg from Mount Sinai School of Medicine found that children born to men over age 40 were 5.75 times more likely to have autism than children born to men under the age of 30. It found no relationship between maternal age and offspring with autism, however.

Reichenberg's study had a big impact when it came out, and it launched many additional studies to confirm its findings. In addition, it sparked studies to further explore whether maternal age is actually irrelevant to the diagnosis of autism spectrum disorder (ASD) in children.

Over more than a decade, multiple studies have confirmed some of Reichenberg's findings while disputing others.

Importance of Father's Age

A major study conducted in Sweden looked at 2.6 million children born between 1973 and 2001. After controlling for many other possible causes, the researchers found that fathers older than 45 at the time of the child's birth are 3.45 times more likely to have children with autism.

The study found older fathers are also far more likely to have children with attention deficit hyperactivity disorder (ADHD), schizophrenia, and bipolar disorder.

Additional studies have, in general, supported Reichenberg's original findings that older fathers are more likely than younger fathers to have children with autism. But these findings don't tell the whole story because additional studies have linked autism in children with advanced age in mothers, as well.

Importance of Mother's Age

Since the early 2000s, several studies have investigated how maternal age factors into the chance of having children with autism. While Reichenberg specifically found no connection, other studies have found a strong connection.

One study concluded that there is a strong independent connection between higher maternal age and autism. According to this study, having a younger father doesn't protect against autism when the mother is over 35.

Paternal and Maternal Age Both Implicated

While early studies identified the negative impact of the father's age, most recent studies have found a connection between advanced age in both parents and the likelihood of having children with autism, including:

• One large study of over 7.5 million births in California affirming the impact of paternal age nevertheless concluded that an increase in the age of the maternal parent had greater implications for ASD risk than an increase in the same number of years in the age of the paternal parent.
• A 2017 meta-analysis of 27 studies found that an increase of 10 years in maternal and paternal age (such as from age 25 to age 35) was associated with an 18% and 21% higher risk of autism.
• Another large study of over 4.9 million births in California concluded that while older parents, in general, increase the risk of autism, "advanced maternal age, rather than paternal age, may pose a greater risk."
  

How Could Parental Age Be Linked to Autism?

There is no clear explanation for the connection between parental age and autism. There are, however, a number of theories about the connection. A few include:

• Genetic mutation: The cells in males that produce sperm for semen are exposed to more potential toxins as a man ages and may acquire more mutations during this time.
• Social issues: If parents are older when they reproduce, it may be because they took longer than most people to find a mate. This may be an indicator of social difficulties that suggest high-functioning autism (those with milder symptoms but who still require some support).
• Socioeconomic level: In general, older parents tend to be wealthier than younger parents. This suggests that older parents may be more likely to seek autism evaluations for children with relatively mild symptoms.

Summary

Studies have shown an association between the parents' ages and the risk of autism in their child. Various studies have looked into whether maternal age or paternal age plays a role, with some differences in the conclusions. In general, the older a parent is at the time of the child's birth, the greater the risk of autism in the child.