Newly identified mutations in SCA19/22 and their dysfunctions

Written by Sophia Leung Edited by Dr. Marija Cvetanovic

While the mutant proteins in SCA19/22 lose part of their innate functions and properties, they also disrupt the key functions of the normal healthy protein.

The underlying mechanism of the hereditary property of SCA19/22 is elusive. In this study, the researchers investigated the molecular properties of four different mutations found in patients with SCA19/22. They looked at how these mutant proteins affect the normal protein if they are both present in the cell. They found that the mutant proteins are not only non-functional (do not work properly), but that in their presence, the normal protein’s function is also diminished. Furthermore, while the production and proper localization of these mutant proteins are found to be defective, they also bring the same decline to the normal protein. This adds to their disease-causing properties. This study is significant in that it offers a molecular investigation into mutant proteins associated with SCA19/22 that was previously lacking. It also provides evidence that may explain the hereditary property of the disease.

A number of mutations in the gene KCND3 has been associated with SCA19/22. The gene makes the voltage‐gated potassium ion (K+) channel subunit KV4.3. In general terms, the gene makes a protein that functions to allow potassium ions to pass through the membrane of nerve cells. Similar to how a flute has many holes to allow air to pass through when played to make a specific note, a nerve cell has different kinds of channels to allow ions to pass through their membrane to orchestrate normal functioning. One could imagine the disruption to any channels, a partial obstruction or a total blockage, could perturb the overall output of the cell.

flute resting on a music stand
Similar to how a flute has many holes to allow air to pass through when played to make a specific note, a nerve cell has different kinds of channels to allow ions to pass through to orchestrate normal functioning. (Photo by Rajesh Kavasseri / Unsplash)

In this study, the researchers found that the normal KV4.3 channel protein detectably allows potassium ions to pass through. But little to no ions can pass through the SCA19/22 mutant KV4.3 channels. Even under the assistance of a “helper” protein, which normally enhances the function of this channel, only one of the mutant channel proteins shows improvement. This indicates that the SCA19/22 causing mutations result in a reduced function of mutated KV4.3 channels.

Continue reading “Newly identified mutations in SCA19/22 and their dysfunctions”

Snapshot: What is Cerebrospinal Fluid (CSF)?

Public transit may not be the first thing that comes to mind when we think about the brain, but it’s a great way to understand how all the parts of the central nervous system work together. Nutrients, hormones, and other important molecules (the passengers) need to get on and off at different stations to do their work. They might first stop at the large internal chambers within the brain, called ventricles. From the ventricles, they can get to the central canal in the spinal cord, as well as the subarachnoid space. The subarachnoid space is a space between two membranes that surround the brain and spinal cord. It provides a stable structure for a network of veins and arteries.

The passengers are shuttled from station to station by the cerebrospinal fluid (CSF), a clear, colourless fluid that provides the central nervous system with necessary nutrients and hormones while carrying away waste products. CSF also cushions the brain and spinal cord by circulating between layers of tissues surrounding them. The whole public transit system is enclosed: the subarachnoid space and the ventricles are connected to the central canal in the spinal cord, forming a single reservoir for CSF.

Cerebrospinal fluid written in colorful letters under a Stethoscope on wooden background
Photo used under license by Sohel Parvez Haque/Shutterstock.com.

CSF is made by the choroid plexus, a collection of tiny blood vessels called capillaries. Capillaries filter the blood and secrete it into the ventricles. When the pressure of CSF is less than the pressure in the capillaries, CSF flows out and into the ventricles. When the pressure of CSF is greater than that of the bloodstream, the extra fluid is absorbed from the subarachnoid space and into sinuses (large areas filled with blood), where it can flow into the surrounding veins. The blood supply in the central nervous system tightly regulates the movement of molecules or cells between the blood and brain. This blood-brain barrier is crucial for protecting the brain from toxins and pathogens. Dysfunction of this specific system contributes to the development of neurological diseases.

Anatomical labeled scheme with human head and inside of skull, including superior sigittal sinus, ventricles, arachnoid Villi and spinal cord central canal.
Structure of the ventricles and central canal components that contribute to the public transit system. Photo used under license by VectorMine/Shutterstock.com.

Why is CSF Important for Neurodegenerative Diseases?

In neurodegenerative diseases like Spinocerebellar Ataxias, CSF contains molecules that can be used as biomarkers. Biomarkers are disease-specific proteins that change in concentration depending on disease stages. Biomarkers provide information on disease progression, with or without the impact of therapeutics. They are also crucial for understanding how disease processes work and assist in developing treatments.

The development of intrathecal injections, injecting into the central canal for distribution to the central nervous system (for example, spinal anesthesia), has been monumental for administering drugs in neurodegenerative diseases. In other words, not only can the public transit system of the central nervous system be investigated to see what passengers are associated with the disease, but it can be used to deliver “medicine passengers” to the place where the disease occurs.

If you would like to learn more about Cerebrospinal Fluid, take a look at these resources by MedlinePlus and WebMD.

Snapshot written by Kaitlyn Neuman and edited by Dr. Tamara Maiuri.

Evaluating the long-term safety of lentiviral gene therapy in SCA3 mice

Written by Dr. Ambika Tewari Edited by Dr. Hayley McLoughlin

Lentiviral expression of an shRNA against ataxin-3 was well-tolerated and produced no measurable adverse effects in wild-type mice.

Evaluating the safety profile is a necessary and crucial step in qualifying a therapy for use in patients. Gene therapy is an experimental technique that has demonstrated tremendous progress in the treatment or reversal of a disease, specifically monogenic disorders. Carefully investigating the safety and tolerance of gene therapy is important to gauge its suitability for clinical trials. Gene therapy tools can be used in different ways to achieve the same therapeutic effect: the faulty gene can be replaced with a healthy copy, the mutated gene can be repaired, or the mutant copy of the gene can be silenced. You can learn more about gene therapy in this pat SCAsource Snapshot.

Spinocerebellar ataxia type 3 (SCA3) or Machado-Joseph disease (MJD) causes progressive loss of neurons in the spinal cord, and several regions of the brain. This includes the cerebellum, brainstem, striatum and substantia nigra. These neurons have crucial functions. Without these neurons, patients experience motor incoordination, loss of balance, and in severe cases, premature death. While great progress continues to be made in understanding how a mutation in a single gene, Ataxin-3, causes the symptoms of SCA3, there is still no treatment to stop the disease progression. As a monogenic disorder, SCA3, like other Spinocerebellar ataxias (SCA), is a promising candidate for gene therapy. While there are no approved gene therapies for SCA yet, there any several research labs and companies working towards achieving this goal.

An artist's drawing of scientists standing infront of a giant piece of DNA and drugs
This is truly an exciting time for gene therapy, but it is also important to keep the safety of patients a top priority. Photo used under license by Visual Generation/Shutterstock.com.

The researchers in this study have been working on gene therapy for SCA3 since 2008. They have researched how gene therapy could offer protection against further decline, in several cell and mouse models of SCA3. They used an approach where they decreased the levels of the mutant Ataxin-3 gene while leaving the normal Ataxin-3 gene intact. This is known as allele-specific targeting. They demonstrated that using this technique, they could significantly reduce the behavioral and neuropathological changes that occur in SCA3 mice. Mice treated with the gene therapy showed improvements in their balance and motor coordination. 

Gene therapy in its most basic form involves two components, the gene that will replace or remove the diseased gene and a vector that will transport this new gene to its site of action. The most commonly used vectors today are adeno-associated virus (AAVs) followed by retrovirus. These viruses have been specifically engineered to deliver their passenger to the specified location. While both vectors have been through several years of preclinical and clinical testing for numerous gene therapy candidates, there are questions that remain regarding their safety. (1) Does the gene therapy product continue to be expressed in the targeted area long-term; (2) If there is long-term expression does it cause any adverse measurable effects to the targeted area; (3) Does the long-term expression affect the normal functioning of the targeted cells/organ.

Continue reading “Evaluating the long-term safety of lentiviral gene therapy in SCA3 mice”

Spotlight: The Kuo Lab

Principal Investigator: Dr. Sheng-Han Kuo

Location: Columbia University, New York, NY, United States

Year Founded:  2012

What disease areas do you research?

What models and techniques do you use?

Kuo Lab group photo.
This is a group picture of the Kuo Lab. From the left to right: Nadia Amokrane, Chi-Ying (Roy) Lin, Sara Radmard, Sheng-Han Kuo (PI), Chih-Chun (Charles) Lin, Odane Liu, Chun-Lun Ni , Meng-Ling Chen, Natasha Desai, David Ruff.

Research Focus

What is your research about?

We study how mishaps and damage in the cerebellum lead to the symptoms experienced by ataxia and tremor patients. By looking at human brains, as well as brains from mouse models, we study how different changes in brain structure can lead to symptoms. This includes how well different parts of the brain can communicate with each other.

Why do you do this research?

When you ask patients about the challenges living with ataxia or tremor, they will talk to you about their symptoms. Symptoms can make different activities of daily living very challenging! By connecting specific brain changes to specific symptoms, we want to develop treatment options that target specific diseases. By doing this, we hope to improve patient’s quality of life. 

Initiative for Columbia Ataxia and Tremor Logo. It is a circle containing a lion with its whiskers to look like a neuron

The Kuo lab is part of the Initiative for Columbia Ataxia and Tremor. It’s a new Initiative at Columbia University to bring a group of physicians, scientists, surgeons, and engineers to advance the knowledge of the cerebellum and to develop effective therapies for ataxia and tremor.

Are you recruiting human participants for research?

Yes, we are! We are looking for participants for clinical research and trials. You can learn more about the studies we are currently recruiting for at this link.

Fun Fact

In the Kuo Lab, we call ourselves “the Protector of the Cerebellum in New York City”.

For More Information, check out the Kuo Lab Website!

We are looking for new graduate students and postdoctoral researchers to join our team. If you are interested in our work, please reach out to us


Written by Dr. Sheng-Han Kuo, Edited by Celeste Suart

Snapshot: What is the Morris Water Maze Test?

Spinocerebellar ataxias (SCAs) are well known for worsening motor coordination symptoms caused by the degeneration of the cerebellum. Yet, increasing reports indicate that broader changes are occurring in the brains of some SCA patients. This includes changes in the hippocampus, a brain region critical for learning and memory. One way to test learning and memory in mice is the Morris Water Maze Test. Researchers use this test on SCA mouse models to investigate how and when learning and memory symptoms arise. More importantly, we can also use this test to evaluate the effect of potential treatments on learning and memory.

white mouse swimming with its head poking up above the water
Although mice can swim quite well, they don’t like swimming. The Morris Water Maze takes advantage of this to test the learning and memory of mice. Photo used under license by Aleksandar Risteski/Shutterstock.com.

The Morris Water Maze consists of a large circular pool of opaque water. A platform is placed in the pool just under the surface of the water so that the mouse won’t be able to see it. Though mice are good swimmers, they don’t particularly enjoy swimming. Mice will always attempt to find the platform as quickly as possible. Shapes on the walls around the pool help the mice orient themselves within the pool (first panel in the figure below).

The first time a mouse swims in the pool (second panel in the figure), the mouse tends to swim aimlessly around until they eventually find the hidden platform. Each subsequent time the mouse swims in the pool, the mouse will get better and better. Using the shapes on the wall to help identify where they are in the pool, the mouse will eventually learn and memorize the platform’s location.

First day, mouse does not know wehere the plaform is an swims a lot. Second day, the mouse still swims a while but remembers where the platform is. On the last day, the mouse knows where the platform is and goes right there.
The three steps in the Morris Water Maze. Image made by Larissa Nitschke use BioRender.

As that happens, they will be better and better at the task. Eventually, the mice will swim immediately to the platform when placed in the pool (third panel in the figure). Researchers can measure this improvement by measuring how much time it takes the mouse to reach the platform and the length of its path to the platform. Additionally, to assess the strength of the memory, researchers can take out the platform from the pool in what is called a “probe trial”. Mice that spend more time in the area where the platform used to be are considered to have built the strongest memories of that location.

As is the case for some SCA mouse models, mice with impaired learning and memory have more difficulty learning and remembering the correct location of the platform. As a result, they spend a longer time searching for and swim longer distances to the platform. Overall, they display a poorer improvement over time. By using the Morris Water Maze Test on SCA models that receive different treatments, scientists can then further test which therapy could improve their learning and memory symptoms. Therefore, the Morris Water Maze Test may help identify new therapeutic strategies to treat learning and memory problems in patients.

If you would like to learn more about the Morris Water Maze, take a look at these resources by the Scholarpedia and JOVE.

Snapshot written by Carrie Sheeler and edited by Dr. Larissa Nitschke.