Revolutionary Research Reveals That Recurrence Risk Of Autism Among Younger Siblings Of Children With Autism Is 2 To 6 Times Greater Than Previously Reported

Jerusalem, August 15, 2011 – Revolutionary research by researchers at the Hebrew University of Jerusalem has revealed that the risk of recurrence of autism among younger siblings of children with autism is two to six times greater than previously reported. The study was published today in the prestigious Pediatrics journal.
 
In this innovative study - the most comprehensive conducted to date - the recurrence risk for autism spectrum disorders (ASD) among infant siblings of children with ASD (that is, the likelihood that a family will have a second child with ASD, if they already have at least one) was examined using the largest sample collected so far and state-of-the-art diagnostic methods.
 
The sample comprised 664 infants, all of whom had at least one older biological sibling with a verified diagnosis of ASD (6% had more than one sibling diagnosed with autism). Infant siblings were enrolled at a very young age, before signs of autism are readily apparent and before parents typically have concerns about development (the infants' mean age was 8 months and two-thirds of the infants enrolled before 6 months of age). Infant siblings were followed longitudinally through 36 months, when symptoms of ASD are present and reliably identified. The researchers used gold standard diagnostic methods and comprehensive developmental assessments were conducted by experts.
 
The main result of the study was that recurrence risk among siblings is 18.7%, which is substantially higher than the results of previous studies, which found a 3% -10% risk of recurrence. Furthermore, the researchers report even higher recurrence rates for infants who fell into certain subcategories of elevated risk: for male infants, a recurrence rate of 26.2% was found (versus 9.1% for female infants). Remarkably, this means that almost one in three male siblings will eventually develop ASD. In addition, recurrence risk for infants with more than one older affected sibling was 32.2% - almost twice the rate of those having one older sibling with ASD.
 
Twelve research groups from the United States and Canada took part in the study. All of the researchers were part of the Autism Speaks funded BSRC (Baby Siblings Research Consortium), an international network of funded studies examining infants in families of children with autism. Prof. Nurit Yirmiya from the department of psychology at the Hebrew University is part of this network and one of the pioneering researchers in this field. The main results of the study indicated that recurrence risk for ASD among younger siblings of children with autism is two to six times greater than the rates found in previous studies.
 
"The higher recurrence rates found in this study in comparison with previous reports resulted from the fact that previous studies were conducted in the 1980’s and 1990’s when different and more narrow diagnostic criteria were used to evaluate children with autism, and there is an overall increase in the number of children who are diagnosed with ASD," says Prof. Nurit Yirmiya.
 
"In addition, previous studies used different assessment methods. For example, in some studies children were not assessed directly and other studies did not control for 'stoppage' (the tendency of parents to limit reproduction after the birth of a child with a disability)."
 
Prof. Yirmiya noted several strengths of the current study, as compared to previous studies: "Only families that had a younger sibling participated; gold standard diagnostic methods as well as comprehensive developmental assessments were used, and administered by experts; this is by far the largest sample to date, pooled across sites so it is a geographically diverse sample. The improved methodology assures that the results of the current study reflect the true population recurrence rates better than previous reports".
 
It should be emphasized that this study is not an epidemiological one but rather a community-based sample of families who voluntarily chose to participate. The fact that families volunteered to participate may explain the higher rates found in the current study.
 
The results of this study suggest the development of young siblings of a child with ASD should be monitored in a rigorous, careful, structured and routine fashion. The study also indicates that sibling status constitutes a significant risk factor for ASD.
 
The researchers say that professionals in the field should work actively and cooperatively with parents to monitor specific developmental milestones and make appropriate intervention plans as needed. Moreover, they say there is a real need to develop preventive programs applicable for infant and toddler siblings of children with ASD who do not yet show the full set of symptoms of autism.