Autism MRI

Source: Brain MR Imaging Findings and Associated Outcomes in Carriers of the Reciprocal Copy Number Variation at 16p11.2

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.

MRI reveals striking brain differences in people with genetic autism

Brain MR Imaging Findings and Associated Outcomes in Carriers of the Reciprocal Copy Number Variation at 16p11.2

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:-

Agenesis of the Corpus Callosum (ACC)                                                                                 

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.

Treatable Chiari 1“brain hernia” present in 7% of Autism

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.

Agenesis of the Corpus Callosum

Today’s post is about another supposedly rare cause of autism called Agenesis of the Corpus Callosum (ACC).

As regular readers of this blog will have noted, extremely rare causes of autism, taken as a group are not so rare after all.  In fact it seems that autism is just a very large collection of somewhat rare biological conditions. 

Of the very few "Autism Dads" I have had a face to face conversation with, one has a child with ACC and another has a son with the even rarer Sotos syndrome. Sotos syndrome is characterized by gigantism, mild ID/MR and often autism. Mutations in the NSD1 gene cause Sotos syndrome

ACC is physical malformation of the brain that shows up clearly on MRI scans and potentially shows up on the mother’s regular ultrasound scans. 

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.

It is suggested by many that a diagnosis of ACC is not compatible with a diagnosis of autism; this just shows a lack of understanding.

Autism is just a description of behaviors, ACC is a biological diagnosis, like Fragile X syndrome or Down Syndrome.  So if a person has autistic behaviors caused by ACC, it is still autism, it is just autism with an explanation of its origin.

The most famous person with ACC was Kim Peek who was the inspiration for the character played by Dustin Hoffman in the well-known film Rain Man.

In addition to having the physical ACC malformation it has been suggested that the cause of ACC in his case was likely FG Syndrome.

Most mutations that cause FG syndrome can be found in the MED12 gene. However, mutations have also been found in FMR1, FLNA, UPF3B, CASK, MECP2, and ATRX genes. Mutations on these different genes lead to the different types of FG syndrome, all with similar characteristics.  Congenital heart defects are common and Peek died of a heart attack aged 58, outlived by his father.  

Agenesis of the Corpus Callosum and broader Autism

Undoubtedly there are people diagnosed with autism, who have undiagnosed ACC, since they never had an MRI scan.  Just like there are many people with autism who have an undiagnosed, but treatable, Chiari “brain hernia”.

It also appears that having a smaller corpus callosum, but falling short of what would be diagnosed as ACC by the MRI scan, is a feature of some people’s autism. You could consider it as partial ACC, like we had partial biotin/biotinidase deficiency.

A very recent paper from the 2016 Society for Neuroscience annual meeting suggested one reason why autism is more prevalent in males.  The study looked at infecting pregnant rats with group B streptococcus to activate the mothers immune system.  Inflammation was then triggered in the fetal side of the placenta, but only in male fetuses.

The males go on to develop brain and behavioral features reminiscent of autism.

Female fetuses were somehow protected and developed normally.  Hopefully Barons Cohen will read this and stop looking for undiagnosed females with autism. There are many good reasons why autism is less prevalent in females, and they are not just “better at hiding it”, as the so-called expert claims. 

 Placenta may hold clues to sex bias in autism

What is interesting is that in the male pups with “autism” they had an unusually thin corpus callosum. It turns out that such minor malformations occur in broader human autism. 

Lack of corpus callosum yields insights into autism

Autism May Involve A Lack Of Connections And Coordination In Separate Areas Of The Brain, Researchers Find

The largest of the white matter tracts is known as the corpus callosum, which allows communication between the two hemispheres (halves) of the brain.
"The size of the corpus callosum was smaller in the group with autism, suggesting that inter-regional brain cabling is disrupted in autism," Dr. Just said.

In essence, the extent to which the two key brain areas (prefrontal and parietal) of the autistic participants worked in synchrony was correlated with the size of the corpus callosum. The smaller the corpus callosum, the less likely the two areas were to function in synchrony. In the normal participants, however, the size of the corpus callosum did not appear to be correlated with the ability of the two areas to work in synchrony.

"This finding provides strong evidence that autism is a disorder involving the biological connections and the coordination of processing between brain areas," Dr. Just said.

Atypical development of white matter microstructure of the corpus callosum in males with autism: a longitudinal investigation.

CONCLUSIONS:

These longitudinal results suggest atypical early childhood development of the corpus callosum microstructure in autism that transitions into sustained group differences in adolescence and adulthood. This pattern of results provides longitudinal evidence consistent with a growing number of published studies and hypotheses regarding abnormal brain connectivity across the life span in autism.

Comments on this study

The study suggests that white matter abnormalities manifest early in autism, says Thomas Frazier, director of Center for Autism at the Cleveland Clinic in Ohio. “It also serves as a nice demonstration that brain abnormalities in autism will become clearest and most helpful for pointing to etiology when we look at them developmentally, longitudinally, rather than at a single age," he says.

The findings do not imply that corpus callosum abnormalities cause autism, cautions Ralph-Axel Müller, professor of psychology at San Diego State University, who was not involved with the work. Rather, any irregularities in the corpus callosum may stem from other abnormalities in the brain that have been associated with autism, Müller says.

Still, changes in the corpus callosum may help to explain why autism symptoms worsen in some individuals and improve in others, Travers says. "Is there some aspect of white matter micro-structure occurring early in the developmental pathology that locks in persistent autism across the lifespan? What are the mechanisms? Can they be unlocked?” she says. “These will be important questions for future research.”

  

Conclusion

It is estimated that at one in 4,000 individuals has a disorder of the corpus callosum. I suspect it is more, but you would need to routinely give MRI scans to people diagnosed with autism to find out.

It is clear that milder disorders of the corpus callosum may be a feature of many people’s autism and those changes over time in the corpus callosum may help to explain why autism symptoms worsen in some individuals and improve in others.