Feb 17 2012
Yet another study showing that clear signs of autism are present as early as six months of age has been published. In this study researchers looked a high-risk children (siblings of children with autism) at 6 months with MRI scanning (specifically diffusion tensor imaging) and then evaluated them clinically at 24 months to see which children met criteria for autism spectrum disorder (ASD). Some of the children also had imaging at 12 months. The imaging was used to look at the development of white matter – the tracks in the brain that contain the axons or pathways of communication.
When compared as groups the 28 infants who went on to develop ASD had significantly decreased white matter development in 12 of 15 brain pathways examined in comparison to the 64 infants who did not develop clinical ASD. These results are very robust, although I should point out that the children were compared as groups, not individuals. The purpose of this study was to see if there were detectable changes in the brains of children with ASD at 6 months, not necessarily to explore its utility as a diagnostic tool that can be applied to an individual.
Still, this study supports other research providing increasing evidence that ASD begins at least as early as 6 months. It is probable that ASD begins earlier than 6 months, actually, because in order for detectable differences to be present in the brain, development must have been heading down a different trajectory prior to that. These kinds of studies have not looked at children younger than 6 months, and it would be interesting to see how early such changes can be detected. But even without that data, we can conclude the whatever process results in ASD it is active prior to 6 months so that the effects are detectable at 6 months.
This study also supports other research that indicates that autism is partly a disorder of communication within the brain – different parts of the brain have decreased communications with each other. It’s nice when several independent lines of evidence all converge on one cohesive story. With regard to ASD, we have evidence that clinical signs of ASD are present as early as six month and changes in brain anatomy are also present as early as 6 months. Further, there is growing evidence that ASD is the result of a complex set of genetic variations. Autism, in other words, is a genetic disease – which is compatible with detection early in infancy.
This research has several implications. It broadens our understanding of the pathophysiology of ASD – exactly what is happening and how does that manifest with the signs of ASD. Further it offers the potential for earlier and more objective diagnosis of ASD. Laboratory support for a clinical diagnosis is always helpful – again, because it allows for multiple independent lines of evidence, and therefore increases confidence. Early diagnosis is also helpful in identifying children who might benefit from special services.
It’s also possible that research such as this will help us identify specific subtypes of ASD, which may have different causes and different clinical needs. ASD, as the name states, is a spectrum – it’s really a group of similar disorders with similar clinical manifestations. It is likely, however, not one discrete entity. The fact that so many different genetic markers have been identified that are associated with ASD supports this view.
And of course I need to point out that research showing that autism begins prior to 6 months of age rules out any environmental exposure after 6 months as a significant cause. The MMR vaccine (the specific vaccine that Andrew Wakefield tried to link to ASD) is typically given at 12 months of age, and so cannot be a significant cause of ASD. As you can see from the immunization schedule, many vaccines are given after 6 months. Some vaccines, however, are given prior to 6 months, so those intent on blaming autism on vaccines can still point to those earlier injections.
There is no evidence to link any vaccine or vaccines in general to the development of ASD or any neurological disorder. Evidence is converging on the conclusion that ASD is a set of genetic disorders. If history is any guide it’s also true that evidence is not likely to sway members of the anti-vaccine community. But more evidence is always nice. There is always uncertainty in science, and the more we can narrow that uncertainty with better evidence, the better we will be able to make the case for the safety of vaccines.
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