One of the many unanswered questions about autism is whether autism is something that a person is born with or whether it is something that happens or develops later. There are currently a few theories about how autism is thought to develop -
Early onset - A child is born with autism and shows subtle signs of it almost from birth. These differences grow over time until the child is noticeably different from "typical" children. It is thought that most people with autism fall into this category.
Regression - A child appears to be developing normally for the first year or two but then has a period where they regress and lose previously acquired skills and become different from other children.
Plateau - A child develops normally, without any early signs of autism or regressions, until they hit a certain point. After this point, they simply simply fail to develop new skills and stop developing normally (i.e. hits a plateau in their development)
That's where a new study, published online this month in the Journal of the American Academy of Child & Adolescent Psychiatry, comes in. This is one of the first studies to follow children and watch which ones develop autism rather than look at which ones developed autism after the fact.
The text of the study is freely available, so if you are interested in the topic I suggest you read it for yourself.
The children included in this study were selected from a larger, ongoing study of infant siblings of children with autism. For this study, researchers selected 25 children who developed autism and 25 that did not. These children came either from a high risk group (sibling had autism) or a low risk group (no siblings with any developmental disorders). Of the 25 children with autism, 22 came from from the high risk group.
Each of these children was evaluated at 6, 12, 18, 24, and 36 months using a variety of tests. The results of the tests were compared to each other and found to be in agreement. Overall, the researchers did a good job getting an accurate picture of how these children developed and what skills they had at each point in time.
The results of the study were interesting, to say the least.
The most important finding was that the children who went on to develop autism were no different from the other children at 6 months. And even more than that, these children seemed to be slightly more social than the other children at 6 months (although this result is not scientifically significant).
For the next 12+ months, the development of children in the autism group slowed down and they failed to keep up with the development of their peers. But more importantly, most of the children showed loss of skills - as in they regressed. In what could be considered a silver lining, the children did not show losses of cognitive ability or language skills as the losses appeared to be of social communication skills area.
The second important part of this study is that most of the parents (83%) did not pick up on these regressions. Keep in mind that these are mostly parent who already had a child with autism and, as such, would be familiar with what autism looks like. It is likely that they would be watching very closely for signs of autism in their younger children. This finding, if confirmed, means that parents frequently miss subtle regressions and signs of autism in their children.
The result of these findings is that our models of how autism develop may be wrong. Autism may not be present from birth in the majority of cases and might start developing sooner than we think and involve more regressions.
The researchers proposed a new theory whereby the symptoms of autism are not prevent at birth but rather appear over a length of time. Under this theory, most children have regressions but it is the timing and severity of the regressions that give the impressions of different models of onset. If the regressions happen early enough they are much harder do detect and make it seem like the symptoms have always been there. If they happen late enough, the results are much more drastic and noticeable and make it seem like it appeared out of the blue.
I think it is important to remember that this is just one study, and a smaller one at that. While the researchers appear to have been very careful these results are still going to need to be confirmed.
But, if the researchers are correct, autism may develop differently than we think.
A Prospective Study of the Emergence of Early Behavioral Signs of Autism
Sally Ozonoff, Ana-Maria Iosif, Fam Baguio, Ian C. Cook, Monique Moore Hill, Ted Hutman, Sally J. Rogers, Agata Rozga, Sarabjit Sangha, Marian Sigman, Mary Beth Steinfeld, Gregory S. Young
Journal of the American Academy of Child and Adolescent Psychiatry 8 February 2010 (DOI: 10.1016/j.jaac.2009.11.009)