Identifying FDA-approved molecules to treat SCA6

Written by Dr Hannah Shorrock Edited by Dr. Larissa Nitschke

Pastor and colleagues identify FDA-approved small molecules that selectively reduce the toxic polyglutamine-expanded protein in SCA6.

Selectively targeting disease-causing genes without disrupting cellular functions is essential for successful therapy development. In spinocerebellar ataxia type 6 (SCA6), achieving this selectivity is particularly complicated as the disease-causing gene produces two proteins that contain an expanded polyglutamine tract. In this study, Pastor and colleagues identified several Food and Drug Administration (FDA) approved small molecules that selectively reduce the levels of one of these polyglutamine-containing proteins without affecting the levels of the other protein, which is essential for normal brain function. By using drugs already approved by the United States Food and Drug Administration to treat other diseases, referred to as FDA-approved drugs, the team hopes to reduce the time frame for pre-clinical therapy development.

SCA6 is an autosomal dominant ataxia that causes progressive impairment of movement and coordination. This is due to the dysfunction and death of brain cells, including Purkinje neurons in the cerebellum. SCA6 is caused by a CAG repeat expansion in the CACNA1A gene. CACNA1A encodes two proteins: the a1A subunit, the main pore-forming subunit of the P/Q type voltage-gated calcium ion channel, as well as a transcription factor named a1ACT.

The a1A subunit is essential for life. Its function is less affected by the presence of the expanded polyglutamine tract than that of a1ACT. The transcription factor, a1ACT, controls the expression of various genes involved in the development of Purkinje cells. Expressing a1ACT protein containing an expanded polyglutamine tract in mice causes cerebellar atrophy and ataxia. While reducing levels of the a1A subunit may have little effect on SCA6 disease but impact normal brain cell function, reducing levels of a1ACT may improve disease in SCA6. Therefore, Pastor and colleagues decided to test the hypothesis that selectively reducing levels of the a1ACT protein without affecting levels of the a1A protein may be a viable therapeutic approach for SCA6.

Colorful pile of medicines in blister packs which color are White, Yellow, Black and Pink pills.
By using drugs already approved by the FDA, the team hopes to reduce the time frame for pre-clinical therapy development. Photo used under license by Wanchana Phuangwan/Shutterstock.com.
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Four diseases, One Gene: CACNA1A

Written by Dr. Judit Pérez Edited by Dr. David Bushart

A new case report describes how a new mutation in the CACNA1A gene causes ataxia with seizures.

Genes and their diseases

Hereditary ataxias are caused by mutations in different genes that affect how different parts of the brain and spinal cord work. Usually, the affected genes predict how one would expect the patient’s clinical signs and symptoms to look. The reverse can also be true. For example, a set of clinical signs and symptoms may raise suspicion of a known genetic disease, which allows doctors to perform focused genetic testing to confirm the diagnosis. These correlations are helpful for doctors and patients in understanding the diagnostic process and disease outlook.

New mutation, new disease

A study by Stendel and colleagues was inspired by a patient who developed ataxia in mid-adulthood that slowly worsened over the next decades of his life. The progression resembled that of spinocerebellar ataxias with repeat expansions in their genes as the culprits. However, when doctors performed the usual genetic testing for ataxia genes, they did not find a match. Nevertheless, suspicion for an ataxia gene playing a role remained high. The patient had experienced seizures as a child (called “absence seizures”), which didn’t entirely fit the picture of known SCAs. Where to go from here? The scientists next broadened their search to include 118 genes that are known to cause ataxia or other diseases that include ataxia symptoms.  To their surprise, they found a previously unidentified mutation in a well-known ataxia gene called CACNA1A.

Human brain digital illustration. Electrical activity, flashes and lightning on a blue background.
CACNA1A is a gene that instructs brain cells to make a protein called Cav2.1, which helps neurons communicate. But now mutations in the CACNA1A gene are now connected to four different diseases. Photo used under license by Yurchanka Siarhei/Shutterstock.com.
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Results of the RISCA study: gaining a better understanding of how ataxia symptoms first appear in at-risk patients

Written By Dr. David Bushart Edited by Celeste Suart

The RISCA study will help researchers design smarter, more efficient clinical trials by teaching us about the very early stages of SCA

Ataxia research has grown significantly in recent years. Although much work still remains, we are gaining a better understanding of how ataxia affects patients. Several exciting, new therapies are currently being studied. These advances would not be possible without the involvement of ataxia patients in clinical research studies. Some clinical studies are drug trials, where patients are enrolled to help researchers determine whether new therapies are effective at treating ataxia. However, other equally important types of clinical studies also exist. Ataxia patients play a critical role in the success of these studies.

What would an ideal treatment for ataxia look like? Ideally, we would be able to treat patients when their symptoms are very mild, or perhaps even before their symptoms appear at all. However, there are several obstacles to developing and testing this kind of hypothetical treatment:

First, it can be hard to know which patients to treat if symptoms are not yet present! There are many people who descend from patients affected by SCA of some kind. They have a 50% chance of being affected. While some of these people have been genetically tested, many have not. This makes it difficult to predict whether they will eventually develop SCA at all.

Second, along those lines, it could be very difficult to predict whether a drug is working to prevent symptoms from appearing if we don’t know precisely when symptoms should appear. It is much easier to tell if a drug is working when it is given to a patient with obvious symptoms – if their symptoms improve, the drug works.

Third, it can be difficult for researchers to enroll enough patients into clinical trials to get a meaningful result. This is complicated by the fact that we don’t know the answers to the first two questions above. Until recently, it remained unclear how a trial to test such a hypothetical treatment would need to be designed.

Thankfully, recent work has helped us better understand the answers to these questions. Results from the RISCA study were recently released. RISCA, which is a prospective, longitudinal, observational cohort study, was designed to study individuals who are at-risk for developing SCA, and how SCA symptoms might first appear.

Doctor and patient discussing something while sitting at the table
The RISCA study was designed to give doctors and patients more information about when ataxia symptoms first start to appear. This information is incredibly important for future ataxia clinical trials. Photo used under license by S_L/Shutterstock.com.
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Spotlight: The Watt Lab

Watt lab logo of a neuron

Principal Investigator: Dr. Alanna Watt

Location: McGill University, Montreal, Canada

Year Founded: 2011

What disease areas do you research?

What models and techniques do you use?

Research Focus

What is your research about?

We are interested in how the cerebellum influences motor coordination in both the healthy brain and in models of disease and aging. By identifying changes in the cerebellum underlying ataxias and aging, we hope to discover new treatments for patients.

Why do you do this research?

We want to understand how the cerebellum works and use this knowledge to understand the changes in the cerebellum that lead to ataxia. As a lab, we are particularly interested in studying rare disorders like SCA6 and ARSACS.

These disorders have limited treatment options. We hope that by understanding how the cerebellum works differently in these disorders, we will be able to identify new treatments to help ataxia patients.

We are also interested in identifying common changes between different types of ataxia, to find out whether treatments identified in one form of ataxia might also help other ataxia patients.

Six slippers with a variety of designs, includes brain cells and mice

Fun Lab Fact

We got together and made our own slippers to keep cozy in our office. If you look at the picture closely you might be able to spot some cells from the cerebellum on some of them!

Image courtesy of Anna Cook.

For More Information, check out the Watt Lab Website!


Written by The Watt Lab, Edited by Celeste Suart

A New Use for Old Drugs

Written by Dr. Amy Smith-Dijak Edited by Logan Morrison

Basic biology helps identify a new treatment for ataxia

Drug design doesn’t always have to start with a blank slate. Sometimes understanding how existing drugs work can help researchers to design new ones, or even to recombine old drugs in new and more effective ways. That’s what the researchers behind this paper did. They investigated the basic biology of three existing drugs: chlorzoxazone, baclofen, and SKA-31.

Two of these – chlorzoxazone and baclofen – are already FDA-approved for use as muscle relaxants, and chlorzoxazone had previously been found to have a positive effect on eye movements in spinocerebellar ataxia type 6. Looking at the results of their experiments, they realized that a combination of chlorzoxazone and baclofen would probably be an effective treatment for ataxia over a long period. They offered this drug combination to patients, who had few adverse effects and showed improvement in their diseasesymptoms. Based on these findings, the researchers recommended that larger trials of this drug combination should be conducted and that people trying to design new drugs to treat ataxia should try to interact with the same targets as chlorzoxazone.

mutliple types of drugs in pill form scattered ac
Can old drugs have potential for new types of treatment? Photo by Anna Shvets on Pexels.com.

When this paper’s authors started their research, they wanted to know more about how ataxia changes the way that brain cells communicate with each other. Brain cells do this using a code made up of pulses of electricity. They create these pulses by controlling the movement of electrically charged atoms known as ions. The main ions that brain cells use are potassium, sodium, calcium and chloride. Cells control their movement through proteins on their surface called ion channels which allow specific types of ions to travel into or out of the cell at specific times. Different types of cells use different combinations of ion channels, which causes different types of ions to move into and out of the cell more or less easily and under different conditions. This affects how these cells communicate with each other.

For example, a cell’s “excitability” is a measure of how easy it is for that cell to send out electrical pulses. Creating these pulses depends on the right ions entering and exiting the cell at the right time in order to create one of these pulses. Multiple types of spinocerebellar ataxia seem to make it difficult for Purkinje cells, which send information out of the cerebellum, to properly control the pattern of electrical signals that they send out. This would interfere with the cerebellum’s ability to communicate with the rest of the brain. The cerebellum plays an important roll in balance, posture and general motor coordination, so miscommunication between it and the rest of the brain would account for many of the symptoms of spinocerebellar ataxias.

Earlier research had found a link between this disrupted communication and a decrease in the amount of some types of ion channels that let potassium ions into Purkinje cells. Thus, this paper’s authors wanted to see if drugs that made the remaining potassium channels work better would improve Purkinje cell communication.

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