Siblings of Autistic Children at a Higher Risk than Previously Estimated

It’s a known fact that the siblings of a child with autism are at an increased risk of being autistic as well, but a recent study—the largest ever performed on the siblings of autistic children—has found that this risk is much higher than previously estimated, especially if the sibling is male.

Previous research led to estimation of an increased risk of autism for siblings of autistic children somewhere between 3% and 10%.

This new study, however—which was conducted by researchers from the United States, Canada, and Israel—showed an increase in risk by 8.7%. If the sibling was a male, the researchers found that the risk climbed up to over 26%, as autism is a disorder that primarily affects boys; further, the risk leapt up to 32% for babies who had more than one older sibling with autism.

The study was led by Sally Ozonoff, professor of psychiatry and behavioral sciences at the MIND Institute at the University of California-Davis, Sacramento.

“This is the largest study of the siblings of children with autism ever conducted,” reportedOzonoff. “It's important to recognize that these are estimates that are averaged across all of the families. So, for some families, the risk will be greater than 18%, and for other families it would be less than 18%. At the present time, unfortunately, we do not know how to estimate an individual family's actual risk."

The researchers studied 664 infants who were the siblings of autistic children. At the beginning of the study, the infants had an average age of eight months. At the age of three, they tested the children for autism.

They found that 132 infants met the criteria for Autism Spectrum Disorder (ASD).

The researchers noted that the male babies were at a much higher chance of being diagnosed with autism, as 26% of the boys involved in the study were diagnosed, whereas only 9% of the girls involved were diagnosed.

Among the child study participants, the overall rate of diagnosed ASD was 18.7%.

The researchers observed that, in families with one older child suffering from autism, the rate of incidence was 20.1%, and in families where more than one sibling had autism, the recurrence rate shot up to 32.2%.

"There is no previous study that identified a risk of recurrence that is this high," said Ozonoff.

Autism is a disorder that is still being investigated thoroughly. The genetics of the condition are being assessed through the study of chromosomal abnormalities in autistic individuals, which involves screening every chromosome for evidence of the disorder.

Collaboratively collected evidence concerning the existence of genes related to autism has been discovered in several chromosomal areas, but presently, researchers are searching for association with the disorder in five specific chromosomes, namely: 2, 3, 7, 15 and X.

This study was published in The Journal of Pediatrics.