Genetic, environmental factors may have similar influence on risk of autism


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The risk of autism may be influenced equally by genetic and environmental factors; in addition, a sibling of a family member with autism has a much higher risk for the disorder.

Autism spectrum disorder (Autism Spectrum Disorders (ASD)) affects almost 1 percent of all children born in the United States and is defined as impairment in social interaction and communication and the presence of restricted interests and repetitive behaviors. Autistic disorder (autism) is the most profound form of Autism Spectrum Disorders (ASD), which aggregates in families (increased risk among members of the same family), but the individual risk and to what extent this is caused by genetic or environmental factors is uncertain, according to background information in the article.

Sven Sandin, M.Sc., of the Karolinska Institutet, Stockholm, Sweden, and colleagues estimated the heritability of Autism Spectrum Disorders (ASD) and risk among family members and assessed the importance of genetic vs. environmental factors by using data of all births in Sweden between 1982 and 2006 (n = 2,049,973). The researchers determined the relative recurrence risk (RRR), which is the relative risk of autism in a participant with a sibling or cousin who has the diagnosis (exposed) compared with the risk in a participant with no diagnosed family member (unexposed).

The study included 14,516 children with Autism Spectrum Disorders (ASD), of whom 5,689 (39 percent) had a diagnosis of autistic disorder. The researchers found a 10-fold increased risk of recurrence among siblings of a family member with Autism Spectrum Disorders (ASD); cousins had a 2-fold increased risk. This pattern was similar for autistic disorder but of slightly higher magnitude.

Among children born in Sweden, the heritability of Autism Spectrum Disorders (ASD) was estimated at approximately 50 percent, as was the environmental influence.

"These findings may inform the counseling of families with affected children," the authors write.

(doi:10.1001/jama.2014.4144; Available pre-embargo to the media at

Editor's Note: Please see the article for additional information, including other authors, author contributions and affiliations, financial disclosures, funding and support, etc.

There will also be an audio author interview available for this study at 3 p.m. CT Saturday, May 3, at

Editorial: The Genetic and Environmental Contributions to Autism

Diana E. Schendel, Ph.D., of Aarhus University, Aarhus, Denmark, and colleagues write in an accompanying editorial that much remains to be understood regarding familial risk for autism.

"Future studies might consider risks from different combinations of diagnoses in the [family member with Autism Spectrum Disorders (ASD)] and sibling; for example, the risk of any Autism Spectrum Disorders (ASD) diagnosis in the sibling of a child diagnosed with autistic disorder, or other combinations of Autism Spectrum Disorders (ASD)-related or comorbid neurodevelopmental diagnoses (e.g., Autism Spectrum Disorders (ASD)-epilepsy combinations)."

"In conclusion, the work by Sandin et al supports appreciation of the importance of genetic factors in Autism Spectrum Disorders (ASD) and adds substantial impetus to the growing attention to environmental influences in Autism Spectrum Disorders (ASD) etiology."

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