By focusing on the identification of common genetic variants, researchers have identified 57 single nucleotide polymorphisms (SNPs) that predict-with a high degree of certainty--the risk that siblings of children with Autism Spectrum Disorder (ASD) will also develop the condition. The findings were presented at the International Meeting for Autism Research.
ASD is among the most common form of severe developmental disability with prevalence rates up to 1 in 88 children. Boys are greater than four times more likely to be diagnosed with ASD, while recurrence risks for the sibling of a child with ASD are estimated at 18.7%. Since multiple studies have shown that early assessment and intervention offer significantly improved long-term outcomes, early identification of children at risk of ASD has become a key goal.
Though many recent studies demonstrate that autism has a genetic basis, the inheritance pattern of ASD in most families is highly complex. While genetic testing for autism has been limited to the identification of copy number variants (CNVs), autism-associated CNVs are found only in approximately 10% of children with ASD.
Researchers seeking an alternative approach to identify biomarkers for autism have focused on a number of common genetic variants--or SNPs --that have been shown to be related to the risk of ASD. While individual SNPs do not cause ASD, recent studies have shown that the presence of a combination of autism-associated SNPs can predict with a high degree of certainty whether a child will develop ASD.
"By looking at a combination of gender-specific, risk-associated, genetic common variants, we were able to identify siblings of children with ASD who have a significantly increased risk of developing autism," says lead author Francois Liebaert, MD, Vice President of Research and Development for IntegraGen, SA, Evry, France, "Earlier identification of siblings of children with autism at increased risk may lead to faster referrals, earlier diagnosis, earlier intervention and better prognosis. We also hope to replicate these findings in families that do not have a child with autism."
These findings build upon earlier identification of eight autism-related SNPs that occur in males and females (Autism risk assessment in siblings of affected children using sex-specific genetic scores) published the February 17, 2011 edition of Molecular Autism.
To determine which SNPs were associated with autism, researchers applied techniques that have been used to analyze other complex diseases. By combining statistical results from genome wide association studies (GWAS) with biological information from multiple sources including databases and scientific literature, the researchers were able to identify and prioritize the SNPs, and develop gender-specific genetic scores to predict the risk of autism.
The study comprised greater than 1,100 families which have more than one child diagnosed with ASD, referred to as multiplex families, including nearly 2,000 affected and 600 unaffected siblings. The male to female ratio for affected children was close to 4.2:1. The discovery cohort included 545 families from the Autism Speaks Autism Genetic Resource Exchange Repository (AGRE). The findings were then replicated in a population comprising 627 families including 339 families from a separate AGRE collection and DNA samples from 288 independent families collected at the University of Washington, Seattle and currently maintained at the University of Pennsylvania.
External collaborators included Gerald Schellenberg, Ph.D. and Beth Dombroski, Ph.D. from the Department of Pathology and Laboratory Medicine at the University of Pennsylvania School of Medicine, Philadelphia, PA and Geraldine Dawson, Ph.D., Professor of Psychiatry at the University of North Carolina, Chapel Hill and Chief Scientific Officer, Autism Speaks.