In the early days of this blog, one medical reader told me that in cases of autism an MRI scan of the brain should appear normal.
This also fits with the idea that once you have a biological diagnosis, you no longer have a case of “autism”. It is only Autism, when it is of unknown origin.
People who have a single gene type of autism actually can have significant variations in brain structure that appear clearly on an MRI. This was the subject of a recent study and the source of the MRI in this post.
Many people with autism have abnormalities at a specific site on the 16th chromosome known as 16p11.2. Deletion or duplication of a small piece of chromosome at this site is one of the most common genetic causes of autism spectrum disorder.
People with deletions tend to have brain overgrowth, developmental delays and a higher risk of obesity.
Those with duplications are born with smaller brains and tend to have lower body weight, but also developmental delays.
For regular readers of this blog there are some interesting points to note.
Agenesis of the Corpus Callosum
The corpus callosum is a wide, flat bundle of fibers about 10 cm long that connects the left and right sides of the brain. It facilitates communication between the two sides of the brain.
Agenesis of the corpus callosum (ACC) is a birth defect in which there is a complete or partial absence of the corpus callosum.
ACC leads to behaviors compatible with a diagnosis of autism or Asperger’s in about half of cases.
Symptoms of ACC vary greatly among individuals, as they do in all types of autism. Seizures are common, some people have poor motor coordination, and some people are non-verbal. My original post on the subject:-
You may recall that in the film Rain Man, Dustin Hoffman’s character was inspired by a man with ACC called Kim Peak. It is now thought that Peak had FG Syndrome and this is what caused his ACC. It appears that his brain adapted and made unusual connections leading to his remarkable memory.
You may recall that in the film Rain Man, Dustin Hoffman’s character was inspired by a man with ACC called Kim Peak. It is now thought that Peak had FG Syndrome and this is what caused his ACC. It appears that his brain adapted and made unusual connections leading to his remarkable memory.
The Corpus Callosum is clearly visible on an MRI.
In 16p11.2. deletion you end up with an overgrown (thick) corpus callosum, while in 16p11.2. duplication you end up with a thin corpus callosum, which equates to a partial Agenesis of the Corpus Callosum.
At least one reader of this blog has a case of partial Agenesis of the Corpus Callosum and as he told me, it is not autism it is ACC.
Chiari 1 “brain hernia”
Another point of interest on the above MRI has been highlighted as Cerebellar Ectopia. Now if they had called it a Chiari malformation, you might have linked it to an old post on this blog.
In people with brain overgrowth and/or a small skull, what happens when there is no space left for a growing brain? Well it appears that pressure builds up and you get a kind of hernia with the brain expanding downwards into the spine.
This is called a Chiari 1 malformation and it seems to be quite common in the types of autism associated with over active pro-growth signalling pathways.
Since 16p11.2 deletion is associated with too much growth (thick corpus callosum, brain overgrowth and obesity) we should not be surprised that they often present with Chiari 1 “brain hernia”, which is treatable and this should improve symptoms.
Conclusion
An MRI can sometimes tell you a lot, when you know what to look for and clearly should be carried out on anyone diagnosed with disabling autism.
Undoubtedly there are other areas of the brain where important variances occur.
This would provide useful data to assign individuals with autism into subgroups and hence improve the chance of finding effective therapy. What works for Peter may help Paul, but what works for Zach probably will not help Amber.