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News

Mounting evidence implicates cerebellum in autism

by  /  6 January 2014

Young children who don’t point at interesting objects or make eye contact may be showing early warning signs of autism. Adults with autism may not shake hands or perform other actions rooted in social skills.

All of these behaviors are, in the most basic sense, movements. Yet a major brain structure tasked with coordinating movements, the cerebellum, has been relatively ignored in studies of autism.

“The traditional notion of the function of the cerebellum was [that it is] primarily contributing to motor control,” says Stewart Mostofsky, director of the Laboratory for Neurocognitive and Imaging Research at the Kennedy Krieger Institute in Baltimore.

In other words, the cerebellum was thought to be responsible only for actions such as walking, reaching and grasping, and pedaling a bicycle. The subtleties of social interaction and language belonged to the cerebral cortex.

But that view is changing, say Mostofsky and others. “There’s an emerging body of data that the cerebellum is important for a lot more than regulating your motor movements,” says William Dobyns, professor of genetic medicine at the University of Washington in Seattle, who cares for children with malformations of the cerebellum. “It regulates your emotions as well — your affective state — and your attention.”

This new view is rooted in observations that individuals with tumors, injuries or birth defects affecting the cerebellum have a range of difficulties, including emotional outbursts, attention problems, difficulty understanding social cues, mood changes and repetitive behaviors. Many of these features are frequently seen in people with autism.

Four studies published over the past year provide genetic and mouse model evidence bolstering a link between the cerebellum and autism-related behaviors. The studies represent disparate dispatches from an emerging field, and don’t yet tell a unified story. But they do suggest that the cerebellum is likely to play a bigger role in autism than many had assumed.

Clique candidates:

In one study published last January, researchers identified cerebellar abnormalities in children who carry a deletion of an autism-linked chromosomal region, 22q131. Deletion of this region causes Phelan-McDermid syndrome, characterized by developmental delay and, often, severe language impairment. Many of these individuals are also diagnosed with autism.

The researchers analyzed brain scans of ten individuals with a 22q13 deletion. Eight of them have a smaller-than-normal vermis, the connection between the two halves of the cerebellum; an enlarged posterior fossa, the cavity the cerebellum sits within; or both, the researchers found. Both of these anomalies have also been identified in people with autism2, 3.

Analysis of the participants’ DNA suggests that two genes in the 22q13 region, PLXNB2 and MAPK8IP2, are most closely linked to cerebellar abnormalities in these individuals.

However, the gene in this region that is most strongly implicated in autism, SHANK3, seems to have less impact on the cerebellum: One participant with a deletion that affects only SHANK3 has a normal cerebellum, the researchers found.

Evidence from one individual is far from definitive, cautions Dobyns, the lead investigator. “At this point, I don’t know whether they’re linked,” he says. But, he adds, the results suggest that cerebellar malformation is part of a cluster of disorders and abnormalities — including autism, schizophrenia, epilepsy, intellectual disability and having a small or absent corpus callosum — that often occur together and may sometimes share an underlying genetic cause.

Another study suggests that not just one or two but whole suites of autism genes are at work in the cerebellum. In this study, published in PLoS Computational Biology in July, researchers analyzed the expression of more than 3,000 genes in the mouse brain, based on data from the Allen Mouse Brain Atlas4. Among these, a group of 26 autism candidate genes is expressed together more than would be expected by chance alone.

That’s not so surprising, says study leader Partha Mitra, professor of neuroscience and theoretical biology at Cold Spring Harbor Laboratory in New York. What’s more unexpected, Mitra says, is that the researchers also identified two ‘cliques,’ or groups of genes with similar expression patterns, that contain a high proportion of autism candidate genes. And both of these cliques are expressed in the cerebellum, the researchers found.

One of the groups includes the autism-linked genes PTCHD1, GALNT13, DPP6 and ASTN2. The other, smaller group includes ASTN2 and RIMS3.

“There has been this emphasis on the [cerebral] cortex” in studies of autism, Mitra notes. “I wasn’t expecting the cerebellum to come out in such a robust way.”

An unpublished analysis by Mitra’s team zeroes in on where in the cerebellum these cliques of autism-linked genes are most active. “We see that these expression patterns appear to be localized in the granule cell layer,” he says.

Granule cells are tiny neurons found tightly packed together in the outer region of the cerebellum. The finding contrasts with other studies that have implicated cerebellar Purkinje cells in autism, but Mitra cautions that this analysis is preliminary.

Purkinje pathways:

In fact, a reduced number of Purkinje cells is one of the most consistent findings from postmortem studies of autism brains. These cells represent the main output of nerve signals from the cerebellum, with elaborately branching neuronal projections that travel to various regions of the cerebral cortex.

The Purkinje cell “may be a particularly vulnerable cell type” says Michael Gambello, chief of medical genetics at Emory University School of Medicine in Atlanta.

Earlier this year, Gambello and his colleagues reported that mice lacking an autism-linked gene, TSC2, in Purkinje cells show social deficits reminiscent of autism5.

The work replicates findings from a study last year showing that removing a closely related gene, TSC1, from Purkinje cells also leads to autism-like behaviors in mice6.

In both studies, researchers found that loss of the gene results in Purkinje cell degeneration. The mutant mice also display increased repetitive behavior and decreased interest in social interaction compared with controls. Finally, both teams showed that rapamycin, a drug that inhibits a signaling pathway boosted by the two genes, prevents Purkinje cell loss and the development of autism-like behaviors in the mice.

“Taken together, it’s very strong evidence for the importance of the TSC genes in Purkinje cell viability, and that somehow the loss of these cells is affecting some important connection between the cerebellum and the rest of the brain,” says Gambello.

Next, Gambello’s team plans to study the effects of removing TSC2 from cells in the thalamus or the prefrontal cortex, two of the brain structures with the strongest connections to the cerebellum.

The prefrontal cortex has been strongly implicated in autism. Parts of it are involved in thinking, planning, memory and social behavior, notes Charles Blaha, director of experimental psychology at the University of Memphis in Tennessee.

Blaha and his colleagues have found that in control mice, stimulating a part of the cerebellum called the dentate nucleus results in release of dopamine in the prefrontal cortex. This occurs through two pathways of roughly equal strength: One goes through a part of the brain called the ventral tegmental area and the other through the thalamus.

“Not too many people have paid too much attention to dopamine and its relationship to autism,” says Blaha. But he points out that this chemical messenger is linked to cognitive functions. Problems with dopamine circuits in the cerebellum could contribute to difficulties with cognitive skills such as theory of mind, learning and memory, which many people with autism struggle with.

Blaha and his colleagues have studied Lurcher mice, which carry a mutation in the gene GRID2 that causes them to lose all of their Purkinje cells over the first two to three weeks of life. They also studied mice that model fragile X syndrome, the most common inherited cause of intellectual disability and autism. Both mouse models have deficits in learning and memory. The researchers reported in Cerebellumin August that the mice also have abnormal dopamine circuits7.

In both sets of mice, stimulating the dentate nucleus results in much lower dopamine release in the prefrontal cortex compared with controls, and in a shift in the relative strength of the two dopamine pathways. The team plans to conduct similar studies in other mouse models of autism.

Some researchers view the many studies on the cerebellum as evidence that the region underlies many features of the disorder.

“Cerebellar dysfunction may be contributing to impaired coordination of social actions in parallel to the ways it contributes to impaired coordination of motor actions,” says Mostofsky, who has found that the degree of motor impairment in individuals with autism is linked to their degree of social impairment.

Others are more circumspect, but say the cerebellum is likely to be important in autism even if it only explains some cases. “We know that autism is such a heterogeneous phenotype,” says Gambello. “I think that there is very likely a percentage of children out there with autism where the cerebellum is playing a major role.”

References:

1.Aldinger K.A. et al. Am. J. Med. Genet. A. 161A, 131-136 (2013) PubMed

2. Courchesne E. et al. N. Engl. J. Med. 318, 1349-1354 (1988) PubMed

3. Courchesne E. et al. Neurology 44, 214-223 (1994) PubMed

4. Menashe I. et al. PLoS Comput. Biol. 9, e1003128 (2013) PubMed

5. Reith R.M. et al. Neurobiol. Dis. 51, 93-103 (2013) PubMed

6. Tsai P.T. et al. Nature 488, 647-651 (2012) PubMed

7. Rogers T.D. et al. Cerebellum 12, 547-556 (2013) PubMed

 


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  • Paul Whiteley

    Thanks for the post.

    Just one more study to add to your post would be that from Jill James and colleagues:

    Complex epigenetic regulation of Engrailed-2 (EN-2) homeobox gene in the autism cerebellum (2013) (open-access)
    http://www.nature.com/tp/journal/v3/n2/full/tp20138a.html

    I can’t claim to understand all the ins-and-outs of the James study but I think they are suggesting “sustained EN-2 overexpression may be due to epigenetic abnormalities in histone methylation patterns that may contribute to Purkinje cell loss in some individuals with autism”. Food for thought??

  • Joe

    Although some of Eric Courchesne’s work is cited in this article, I don’t think this article gives enough background on his early work and ideas in this area. Specifically, not only the finding of cerebellar abnormalities is not new, but the idea that the cerebellum is involved in higher cognitive functions is not new either. Some info on this below, but Courchesne expanded on these ideas throughout the 1990s and early 2000s.

    Neuroanatomic imaging in autism.
    Courchesne E.
    Pediatrics. 1991 May;87(5 Pt 2):781-90.

    Abstract
    Based on neuroimaging and autopsy research, in autism no common site or type of abnormality appears in the cerebral hemispheres, thalamus, lenticular nuclei, and caudate nucleus. Nonetheless, further imaging and autopsy studies on this issue can be anticipated. Limbic system abnormalities have been reported at autopsy by one laboratory but not another, and no abnormality was found by the one quantitative MR study to measure a limbic structure. More autopsy and imaging research on the limbic system is needed. The cerebellum is the only anatomical structure for which there is both imaging and autopsy evidence of abnormality based on data gathered by many laboratories. Also, the only autopsy study to conduct statistical analyses of cerebellar cell loss found statistically significant Purkinje cell loss in both the vermis and hemispheres. Despite this, normal findings on routine radiologic examination are not of diagnostic significance at this time. On the one hand, the autopsy data show that most, if not all, autistic individuals have cerebellar cell loss, but on the other, research shows that MR images of the cerebellum in a substantial proportion of autistic individuals (perhaps 20% to 50%) will be indistinguishable from normal. Thus, it is likely that MR technology is not yet sufficiently sensitive to detect cerebellar abnormalities in all autistic persons who have them. Finally, the cerebellum seems an unlikely site of damage for a developmental disorder of higher cognition such as autism. However, new neurophysiologic and neuropsychologic studies of children with hemicerebellar resections and children with hemicerebellar resections and children with autism present an entirely new picture of the role of the cerebellum in normal human cognition in general and in the development of the social and communication deficits in autism in particular. These studies show that autistic subjects and patients with acquired cerebellar damage are unable to rapidly shift their mental focus of attention.

  • ASD Dad

    In 2005 the seminal paper by Vargas / Pardo and Colleagues at Johns Hopkins showed clearly neuroglial activation and neuroinflammation in ASD brains.

    Of particular note was the findings there was an “active neuroinflammatory process in the cerebral cortex, white matter, and notably in cerebellum of autistic patients.”

    Other significant work (ie Geschwind) has shown key genetic pathways involving inflammatory and immune system dysfunction in ASD children and adults.

    “One module was made up of genes in a brain pathway involved in neuron and synapse development, which were under-expressed in autism. Many of these genes were also implicated in autism in previous, genome-wide studies. So, several different lines of evidence now converge, pointing to genes in this M12 module (see picture below) as genetic causes of autism.

    A second module of co-expressed genes, involved in development of other types of brain cells, was over-expressed in autism. These were determined not to be genetic causes of the illness, but likely gene expression changes related to secondary inflammatory, immune, or possible environmental factors involved in autism. “

    http://www.nih.gov/news/health/jun2011/nimh-02.htm

    How far down the raod are we to understanding and publicizing that Autism is a relationship between genes and environment rather than eith single entity ?

  • ASD Dad

    Converging Pathways in Autism Spectrum Disorders: Interplay between Synaptic Dysfunction and Immune Responses

    http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3819618/

  • Rose

    http://www.grandin.com/inc/squeeze.html Temple Grandin speaks to cerebellar abnormailities.

  • Rose

    Also, brought up by Dr. Batra at the 2014 IACC meeting on Jan.14 (not sure correct date, but January meeting), Teitelbaum was brought up. This study, http://www.pnas.org/content/95/23/13982.full.pdf knocked me over. Visual proof, cerebellar-limbic involvement highlighted.

  • Liz

    No one is looking at Pediatric Neurotransmitter disorders and the overlaps with ASD. There are known disorders with dopamine deficiencies in csf that affect far more than just motor skills, and share characteristics of autism. And the few adolescents with ASD and regressive Catatonia who have been evaluated are showing csf deficiencies in HVA, 5HIAA, and/or 5MTHF. Since 5MTHF is critical to the production of these other neurotransmitters, this should be part of the analysis as well.

  • usethebrainsgodgiveyou

    Cerebellum injury at birth leads to a child more likely to displayautism symptoms later on…. 36X more likely …out yesterday

    “Princeton University researchers offer a new theory that an early-life injury to the cerebellum disrupts the brain’s processing of external and internal information and leads to “developmental diaschisis,” wherein a loss of function in one brain region leads to problems in another. Applied to autism, cerebellar injury could hinder how other areas of the brain interpret external stimuli and organize internal processes. Based on a review of existing research, the researchers found that a cerebellar injury at birth can make a person 36 times more likely to score highly on autism screening tests, and is the largest un-inherited risk (above).” (visual graph)

    http://www.princeton.edu/main/news/archive/S40/93/21G13/index.xml?section=topstories

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