ASF Scientific Advisory Boardmember and High Risk Baby Siblings Research Consortium (BSRC) founder Dr. Eric London provides his unique perspective on the recent ASD sibling re-occurance study. You can click here to read the study’s abstract and here to read the ABC News article.
One of the most agonizing decisions which families who have a child diagnosed with autism have to make is whether or not to have other children. Some families easily decide to assume the risk of having more children with autism; however, other families are more reluctant to go ahead and are in need of counseling for this decision. As opposed to other developmental disorders where genetic screening tests are available, the best that genetic counselors can do is to offer the overall re-occurrence rates for autism.
Ozonoff et al., in the September issue of Pediatrics in their publication Recurrence Risk for Autism Spectrum Disorders: A Baby Siblings Reseach Consortium Study, present the data accumulated from this consortium. In this 12 site study 664 infant siblings of already diagnosed older siblings with autism were studied. The main finding is that 18.7% of the infants developed Autism or PDD-NOS. This is in contrast to the previously quoted numbers of 3-10% — although the generally quoted figure was about 5%.
It is very likely that this study is producing more a more accurate assessment of the true reoccurrence rate in a family.
One large factor is that in studies of the general population, the phenomena of “stoppage”, or families who elect not to have more children, makes the numbers of younger siblings with autism artificially lower than the real risk of a family who elects continue to have children. However, in this sample “stoppage” is not a factor. A second advantage of this study is that it is the largest study to date on this topic.
A limitation of the study is that the mean age of enrollment in the study was at the age of 8 months. The authors address this issue by noting that the age of enrollment was not related to the outcome. However, it would seem that parents who are noting some problems in development might be more likely to enroll in the research programs. The authors comment on this by saying they doubt that problems will be recognized by the parents at this early age (2/3 enrolled by 6 months of age) however I would not underestimate the ability of a parent with one autistic child to pick up on even very subtle developmental anomalies.
Also, this study (like most clinical studies of autism) cannot account for the heterogeneity of autism In fact, those families with 2 autistic older siblings had a 32% chance of having the infant sibling become autistic. Whether this is because of a particular genetic predisposition or some yet unknown environmental risk that has a greater effect on that family, the individualization of counseling for a given family is still difficult due to our continued lack of knowledge of the etiology of the various autisms.
Overall this publication provides a very valuable higher estimate of the re-occurrence risk which has immediate value to the community.