Neurologists finds potential route to better treatments for Fragile X, autism

October 23, 2013, University of North Carolina Health Care

When you experience something, neurons in the brain send chemical signals called neurotransmitters across synapses to receptors on other neurons. How well that process unfolds determines how you comprehend the experience and what behaviors might follow. In people with Fragile X syndrome, a third of whom are eventually diagnosed with Autism Spectrum Disorder, that process is severely hindered, leading to intellectual impairments and abnormal behaviors.

In a study published in the online journal PLOS ONE, a team of UNC School of Medicine researchers led by neurologist C.J. Malanga, MD, PhD, describes a major reason why current medications only moderately alleviate Fragile X symptoms. Using mouse models, Malanga discovered that three specific drugs affect three different kinds of that all seem to play roles in Fragile X. As a result, current Fragile X drugs have limited benefit because most of them only affect one receptor.

"There likely won't be one magic bullet that really helps people with Fragile X," said Malanga, an associate professor in the Department of Neurology. "It's going to take therapies acting through different receptors to improve their behavioral symptoms and intellectual outcomes."

Nearly one million people in the United States have Fragile X Syndrome, which is the result of a single mutated gene called FMR1. In people without Fragile X, the gene produces a protein that helps maintain the proper strength of synaptic communication between neurons. In people with Fragile X, FMR1 doesn't produce the protein, the synaptic connection weakens, and there's a decrease in synaptic input, leading to mild to severe learning disabilities and behavioral issues, such as hyperactivity, anxiety, and sensitivity to sensory stimulation, especially touch and noise.

More than two decades ago, researchers discovered that – in people with mental and behavior problems – a receptor called mGluR5 could not properly regulate the effect of the , glutamate. Since then, pharmaceutical companies have been trying to develop drugs that target glutamate receptors. "It's been a challenging goal," Malanga said. "No one so far has made it work very well, and kids with Fragile X have been illustrative of this."

But there are other receptors that regulate other neurotransmitters in similar ways to mGluR5. And there are drugs already available for human use that act on those receptors. So Malanga's team checked how those drugs might affect in which the Fragile X gene has been knocked out.

By electrically stimulating specific brain circuits, Malanga's team first learned how the mice perceived reward. The mice learned very quickly that if they press a lever, they get rewarded via a mild electrical stimulation. Then his team provided a molecule that acts on the same reward circuitry to see how the drugs affect the response patterns and other behaviors in the mice.

His team studied one drug that blocked dopamine receptors, another drug that blocked mGluR5 receptors, and another drug that blocked mAChR1, or M1, receptors. Three different types of neurotransmitters – dopamine, glutamate, and acetylcholine – act on those . And there were big differences in how sensitive the mice were to each drug.

"Turns out, based on our study and a previous study we did with my UNC colleague Ben Philpot, that Fragile X mice and Angelman Syndrome mice are very different," Malanga said. "And how the same pharmaceuticals act in these mouse models of Autism Spectrum Disorder is very different."

Malanga's finding suggests that not all people with Fragile X share the same biological hurdles. The same is likely true, he said, for people with other autism-related disorders, such as Rett syndrome and Angelman syndrome.

"Fragile X kids likely have very different sensitivities to prescribed drugs than do other kids with different biological causes of autism," Malanga said.

Explore further: Study justifies L-DOPA therapy for Angelman syndrome

More information: dx.plos.org/10.1371/journal.pone.0077896

Related Stories

Study justifies L-DOPA therapy for Angelman syndrome

November 12, 2012
Last year a clinical trial of L-DOPA—a mainstay of Parkinson's disease therapy—was launched for Angelman syndrome, a rare intellectual disorder that shares similar motor symptoms such as tremors and difficulty with balance. ...

Fragile X study offers new drug hope

September 24, 2012
(Medical Xpress)—An experimental drug can improve sociability in patients with fragile X syndrome and may be helpful as a treatment for autism, according to a study.

Genetic mutation found to restore translational balance in mice

October 20, 2013
In a biological quirk that promises to provide researchers with a new approach for studying and potentially treating Fragile X syndrome, scientists at the University of Massachusetts Medical School (UMMS) have shown that ...

Next-generation treatments for Fragile X syndrome

November 29, 2012
A potential new therapeutic strategy for treating Fragile X syndrome is detailed in a new report appearing in the current issue of Biological Psychiatry, from researchers led by Dr. Lucia Ciranna at University of Catania ...

Neuroscientists find that two rare autism-related disorders are caused by opposing malfunctions in the brain

November 24, 2011
(Medical Xpress) -- Most cases of autism are not caused by a single genetic mutation. However, several disorders with autism-like symptoms, including the rare Fragile X syndrome, can be traced to a specific mutation. Several ...

Recommended for you

Epilepsy linked to brain volume and thickness differences

January 22, 2018
Epilepsy is associated with thickness and volume differences in the grey matter of several brain regions, according to new research led by UCL and the Keck School of Medicine of USC.

Research reveals atomic-level changes in ALS-linked protein

January 18, 2018
For the first time, researchers have described atom-by-atom changes in a family of proteins linked to amyotrophic lateral sclerosis (ALS), a group of brain disorders known as frontotemporal dementia and degenerative diseases ...

Fragile X finding shows normal neurons that interact poorly

January 18, 2018
Neurons in mice afflicted with the genetic defect that causes Fragile X syndrome (FXS) appear similar to those in healthy mice, but these neurons fail to interact normally, resulting in the long-known cognitive impairments, ...

How your brain remembers what you had for dinner last night

January 17, 2018
Confirming earlier computational models, researchers at University of California San Diego and UC San Diego School of Medicine, with colleagues in Arizona and Louisiana, report that episodic memories are encoded in the hippocampus ...

Recording a thought's fleeting trip through the brain

January 17, 2018
University of California, Berkeley neuroscientists have tracked the progress of a thought through the brain, showing clearly how the prefrontal cortex at the front of the brain coordinates activity to help us act in response ...

Midbrain 'start neurons' control whether we walk or run

January 17, 2018
Locomotion comprises the most fundamental movements we perform. It is a complex sequence from initiating the first step, to stopping when we reach our goal. At the same time, locomotion is executed at different speeds to ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.