How genetic is autism?
According to a new study published by JAMA Pediatrics, children with older siblings who have been diagnosed with autism are seven times more likely than other children to have the disorder themselves.
Autism spectrum disorders (ASDs) are a range of developmental neurological disorders which are linked to social impairment and communication difficulties. They include classic autism, Asperger syndrome, Rett syndrome, pervasive developmental disorder – not otherwise specified (PDD-NOS) and childhood disintegrative disorder. According to the Center for Disease Control, one in every 88 children has an ASD.
The study, which was conducted by Aarhus University in Denmark, tracked the birth and psychiatric registries of 1.5 million Danish children born between 1980 and 2004 and the rate of autism among the surveyed population through 2010.
The researchers found that of the 130,000 children born during that time with an ASD, nearly 300 had an older sibling with the same disorder. Statistically, these younger siblings of children on the autism spectrum were found to be about seven times more likely than other children to be on the autism spectrum themselves.
In addition, children who shared the same mother with an autistic older half-sibling were found 2.4 times more likely than other children to place on the spectrum.
“This study reports siblings diagnosed with an autism spectrum disorder, at a slightly lower rate than reported in past studies,” notes Laura Mulford, PhD, a child psychologist at the Pediatric Developmental Center at Advocate Illinois Masonic Medical Center in Chicago. “Autism spectrum disorders are complex neurological disorders and we’ve known for some time that there is a genetic piece involved, but this estimate is somewhat more conservative than we’ve seen in the past.”
An exact gene that is responsible for autism spectrum disorders has not yet been identified; however, experts at the National Institute of Neurological Disorders and Stroke (NINDS) are in agreement that genetics are at work.
Environmental factors, such as increased parental awareness of the symptoms of autism with one child already diagnosed, may also play a role in these shared sibling diagnoses, according to the NINDS.
“Often families ask about the risk of having another child diagnosed with an autism spectrum disorder, and general figures such as this one are useful pieces of information for families to have,” Dr. Mulford adds. “But keep in mind that this figure does tend to slightly fluctuate and overall while there is an increased risk due to family history, there are several factors that influence whether or not another child would have an autism spectrum disorder.”
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