Tuesday 6 December 2011

Brain enlargement and regression in autism

I will warn you that I have blogged about this research before. By 'this research' I mean the latest paper from Christine Wu Nordahl and colleagues* from the MIND Institute and Harvard University. The paper suggested that brain enlargement, a feature mentioned more than once in autism research, might be tied into a specific type of autism characterised by symptom onset with regression of previously acquired skills. The blog post in question was on the presentation of possible biological phenotypes in autism; that is sub-groups of people with autism with shared, homogeneous biological findings. Homogeneous is not normally a word used in autism and even now I use it very sparingly.

OK lets take a step back. Regression associated with the onset of autistic symptoms is a topic previously covered on this blog. The summary of that post was that for a long time, the general idea was that regression (a loss in previously acquired skills) seemed not to be possible in cases of autism. This then changed to 'of course its possible' and the detailing of quite a few different kinds of regression including the concept of delays + regression. There is still some debate on how widespread regression is in autism and the best criteria to score regression (language, behaviour, adaptive skills, etc). Having said that with the rise of the digital age and the fact that most parents these days have a photographic and video archive of their child's growth and development from very early ages, the process is made slightly easier to examine.

Head size and growth have also been discussed in relation to autism. The general consensus being that larger heads and early accelerated brain growth shows more than a passing connection to cases of autism but with some interesting ethnic variables and certainly, by no means, an exclusive phenomenon to just autism.

So putting head size and regression together, Nordahl and colleagues present the results of a small, but quite important study which in my humble opinion charts the future course for autism research, looking at smaller sub-groups with shared commonalities. The paper itself is open-access but here is a brief summary:

  • Participants were enrolled as part of the Autism Phenome Project and included 114 children with autism. Controls (n=66) were matched for age and gender (well perhaps not so much for gender).
  • Children with autism were divided into two groups: regression (n=61) and non-regression (n=53) with regards to their symptom onset history using the ADI-R. Before you say ADI-R...mmm, there was some other follow-up to determine the presence of regression or not. 
  • Imaging scans were conducted to ascertain total cerebral (brain) volume which was accompanied by inspection of infant records charting head circumference.
  • Results suggested a few things: brain enlargement is not consistent across all cases of autism but perhaps showing slightly more connection to those cases where regression in onset was cited. Having said that brain enlargement seemed to be more of a boy than girl thing and there was a large amount of overlap between the autism and control groups. Head circumference measurements showed that head enlargement in cases of autism appeared to become more pronounced after about 4 months of age and between 6-13 months of age, there was some clear water in measurements comparing the autism-regression vs. the autism-non-regression and control groups. The regression group showing larger measurements.

Allowing for the relatively small participant numbers and the reliance on stock items from the ADI-R to denote regression or not, this is an interesting paper. If we add these findings to that of the recent neuron counting in the prefrontal cortex data allowing for difference in things like age, a very fuzzy picture starts to emerge of when and possibly where brain overgrowth might occur in some cases of autism.

More of this phenotype research please.

* Nordahl et al. Brain enlargement is associated with regression in preschool-age boys with autism spectrum disorders. PNAS. November 2011.

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