Sharing a Womb and Sharing Autism

Siblings of autistic individuals are more likely to develop autism, according to a population study

/ Author:  / Reviewed by: Robert Carlson, M.D Beth Bolt, RPh

Although the exact cause of autism is unknown, genes are thought to play a role. For that reason, siblings and some half-siblings of individuals with autism may be at a higher risk for developing autism, according to recent research.

A new study used information from a database to look at the risk of autism between siblings.

The researchers found that the sibling of a person with autism was more likely to have autism themselves than a person without an autistic sibling. Half-siblings of a person with autism were also more likely to develop autism if they have the same mother.

This study suggests that genetics play a significant role in autism, especially among family members who shared the same womb.

"Be aware of the symptoms of autism in children."

Therese Gronberg, MSc, Diana Schendel, PhD, and Erik Parner, MSc, PhD, conducted this study in order to examine the risk of recurrence of autism spectrum disorders among half- and full siblings.

People with autism spectrum disorders typically have difficulty with social interactions and communication. They also commonly have very specific interests and engage in repeated behaviors.

Approximately 30 percent of patients with autism are children. Autism in children is usually referred to as "childhood autism." About 1 percent of the population has autism, but diagnoses are becoming more common.

The cause of autism is unknown, but some genetic factors are likely involved in the development of autism.

This research is the first population-based study to estimate autism recurrence in siblings. The researchers used the Danish Medical Birth Registry to gather information about all the children born in Denmark between 1980 and 2004. All cases of autism spectrum disorder were registered in the Danish Psychiatric Central Register.

Using the information from both registries, the researchers were able to statistically evaluate the recurrence risk of autism for full- and half-siblings. The researchers also paid close attention to whether the older sibling had been diagnosed with autism.

The researchers found that 13,164 of the children, or 1.2 percent of the children born during the 24-year period, had been diagnosed with autism.

People with an older sibling who had been diagnosed with autism spectrum disorder were about seven times more likely to be diagnosed as well, compared to people whose older siblings did not have autism. For childhood autism, the recurrence risk doubled.

A person with a maternal half-sibling with autism was 2.4 times more likely to develop autism than the overall population.

A person who shared a father with an autistic half-sibling, on the other hand, was not significantly more likely to develop autism. 

The authors said that parents with an autistic child may be more aware of the symptoms of autism, leading to higher diagnoses. However, the genetic component of autism is still thought to be strong.

Half-siblings who share a mother may be more likely to have autism than half-siblings who share a father because they share one quarter of their genes and were exposed to the same environment in the womb.

"This important study, made possible because of the medical registries in Scandinavian countries such as Denmark, affirms what others have found: autism has a significant genetic component, so having one autistic child increases your risk of having another," said Glen Elliott, PhD, MD, a Clinical Professor (Affiliated) at the Stanford University Department of Psychiatry and Behavioral Sciences, Emeritus Professor of Clinical Psychiatry at the University of California, San Francisco, and Chief Psychiatrist and Medical Director at Children's Health Council.

"It also hints, as the authors discuss, at maternal environmental factors as well as genetic factors, although what those are still remains to be established," said Dr. Elliott.

The research was published in JAMA Psychiatry on August 19. 

The study was funded by Aarhus University. The authors disclosed no conflicts of interest.

Review Date: 
August 27, 2013
Last Updated:
August 28, 2013