Sunrise of Gene Therapy for Friedreich’s Ataxia

Written by Dr. Marija Cvetanovic   Edited by Dr. Ronald Buijsen

Researchers from the University of California show they can “edit” the Frataxin gene in human cells from Friedreich’s Ataxia and transplant them into mice. This lays the groundwork for this method to be tested for safety.

Friedreich’s ataxia is a progressive, neurodegenerative movement disorder. It is often associated with heart issues and diabetes. Symptoms first start to appear in patients when they are around 10 to 15 years old. Friedreich’s ataxia has the prevalence of approximately 1 in 40,000 people and is inherited in a recessive manner. This means that patients with Friedreich’s ataxia inherited a disease gene from both the father and mother. Friedreich’s ataxia is caused by an overexpansion of the GAA repeat in the Frataxin gene, all these extra repeats causes less Frataxin protein to be made.

Human hematopoietic stem and progenitor cells (HSPCs) are the stem cells that give make to other types of blood cells. You can find HSPCs in the blood all around the body.

HSPCs are ideal candidates for use in stem cell therapy because of a few reasons. First, you can easily get them out of the body through a blood donation (at least easier than some other types of cells!). Second, they can self-renew, meaning they will make more of themselves. Third, other folks have researched this type of cell before, so we know they are fairly safe. Researchers wanted to test if these cells could be used to help treat Friedreich’s ataxia.

CRISPR-Cas9 is a customizable tool that lets scientists cut and insert small pieces of DNA at precise areas along a DNA strand. The tool is composed of two basic parts: the Cas9 protein, which acts like the wrench, and the specific RNA guides, CRISPRs, which act as the set of different socket heads. These guides direct the Cas9 protein to the correct gene, or area on the DNA strand, that controls a particular trait. This lets scientists study our genes in a specific, targeted way and in real-time.
Researchers used CRISPR editing to fix the mutation causing Friedreich’s ataxia in patient blood cells. Photo Credit: Ernesto del Aguila III, National Human Genome Research Institute, National Institutes of Health
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Repeat interruptions are associated with epileptic seizures in SCA10

Written by Dr Hannah Shorrock  Edited by Larissa Nitschke

Repeat interruptions in SCA10 influence repeat tract stability and are associated with epileptic seizures

Multiple spinocerebellar ataxias (SCAs) are caused by repeat expansion mutations, but in some cases, these repeat expansions are interrupted. The presence of repeat interruptions can influence disease symptoms and how the repeat expansion behaves. This is the case for SCA10. Some patients with SCA10 have a series of repeat interruptions, which are referred to as an ATCCT repeat interruption motif. In SCA10 patients with this interruption motif, Dr. Ashizawa and his team found an increased risk of developing epileptic seizures and identified that the interruptions influence the local stability of the repeat expansion.

A cartoon of a DNA molecule with light radiating from it
Small interruptions in the ATXN10 gene may affect the likelihood of SCA10 patients developing epileptic seizures

SCA10 is a dominantly inherited ataxia caused by an ATTCT repeat expansion in the Ataxin 10 gene (ATXN10). Unaffected individuals usually carry 9-32 ATTCT repeats, while SCA10 patients carry an expansion of up to 4500 repeats. SCA10 patients suffer from cerebellar ataxia, but some patients also have other symptoms, including epileptic seizures. Dr. Ashizawa and his team were interested in why some patients with SCA10 suffer from epileptic seizures, but others do not.

Initially, the group investigated whether the length of the ATXN10 repeat expansion correlated with epileptic seizures. They found no difference in repeat length between 37 SCA10 patients who developed epilepsy and 51 who did not. This shows that repeat length does not influence whether or not SCA10 patients develop epileptic seizures.

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Targeting protein degradation to alleviate symptoms in MJD

Written by Ambika Tewari   Edited by Brenda Toscano Márquez

Trehalose, a natural autophagy inducer shows promise as a therapeutic candidate for MJD/SCA3

Every cell has an elaborate set of surveillance mechanisms to ensure optimal functioning. As proteins are synthesized, errors can occur leading to misfolded proteins. These abnormal proteins can be harmful to the cell. For this reasons it is important to monitortheir occurrence and decide whether they should be degraded.  Autophagy is one way that these misfolded proteins can be degraded. Autophagy literally means self-eating and serves as a quality control mechanism. Defects in autophagy have been linked to several neurodegenerative disorders.

Machado-Joseph disease (MJD) or spinocerebellar ataxia type 3 is caused by an abnormal expanded CAG repeat in the ATXN3 gene. This CAG expansion causes misfolding of the ataxin-3 protein. The now unstable ataxin-3 is prone to forming aggregates in cells of some regions of the brain including the cerebellum, brainstem and basal ganglia. The accumulation of ataxin-3 in the cell leads to the progressive loss of neurons in the affected brain regions.

Normal ataxin-1 proteins becomes misfolded due to CAG expansion, but autophagy with proteins LC3B and Beclin-1 should degrade and break down misfolded ataxin-3
A diagram of how autophagy should break down abnormal expanded ataxin-3. But what happens when this break down doesn’t happen? Diagram by  Ambika Tewari using BioRender.

Researchers, eager to help patients with MJD, began to question why would the cellular surveillance system allow this toxic accumulation of misfolded ataxin-3. Surely there are mechanisms, like autophagy, to prevent this from occurring. This led to a number of studies that found that autophagy is defective in MJD patients. This was also confirmed in different mouse and cell models of MJD. In fact, earlier studies by the lab of Dr. Luís Pereira de Almeida found that increasing the amount of an autophagy protein (beclin-1) in the brain of an MJD mouse model improved some of the behavioral and neuropathological deficits. Together, these studies have provided evidence that autophagy may serve as a therapeutic target for MJD.

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Snapshot: What is Polymerase Chain Reaction (PCR)?

Polymerase chain reaction, or PCR, is a commonly used laboratory technique that was invented in the 1980s. The method has many applications in different fields, ranging from identifying individuals in forensic science, detecting pathogens in water supply, and genetic testing in medicine.

PCR works by first obtaining a sample that contains genetic information (DNA) such as blood. Then using a specialized enzyme called “DNA polymerase”, researchs can amplify and make billions of copies of a specific segment within the DNA that they are interested in (the region of interest). Because of this amplifying capacity, PCR is a very sensitive test and can be useful to detect even small trace amounts of DNA in a sample.

A DNA double helix rests on a print-out illustration of the DNA letters A, T, C and G.
PCR can help us read the genetic code of specific segments or regions of interest. Photo Credit: Darryl Leja, NHGRI.

By producing billions of copies of DNA, it also makes it possible for scientists to analyze the region of interest. To amplify only the region of interest within the original DNA sample, scientists design and use “primers”. Primers are very short single-stranded DNA sequences specifically designed to match up with a specific region of interest within the DNA. Two primers are used because one is for the beginning of the sequence, and the other is for the end.

How is a PCR test done in the lab?

To perform the PCR reaction in the laboratory, scientists mix the genetic sample, the primers, some nucleotides (the building blocks of DNA), minerals (such as magnesium), and the important enzyme DNA polymerase in a small test tube. The test tube is put into a thermocycler, a device that can quickly and accurately change temperatures. In order for the DNA replication process proceed, there needs to be mutiple suddent changes in tempurature.

A visual depicition of the PCR process, it is described in a step-by-step process in the text.
A diagram depicting the steps during Polymerase Chain Reaction (PCR). Image by Nola Begeja.

The first step of the cycle is called “denaturation”. This is where the genomic DNA from the sample is melted to a very high temperature of 96 °C. This makes the double-stranded DNA becomes single-stranded.

The next step is called “annealing”, where the temperature is reduced to 55 °C. This lets the primers can bind to the region of interest within the single-stranded genomic DNA.

Then, “elongation” occurs where the temperature is raised to 72 °C. This allows the DNA polymerase to effectively replicate the DNA bound by primers to synthesize double-stranded DNA by adding nucleotides. This process cycles from 20-40 times, and each cycle exponentially increases the quantity of DNA.

How is PCR used in ataxia research and treatment?

Certain types of ataxia have specific mutations to DNA that cause disease. For example, some types of spinocerebellar ataxia are caused by a type of mutation called polyglutamine expansion. The tests used to diagnose these types of ataxia use PCR to check to see if the mutations are there. Researchers also use PCR to confirm that cells, animals, or humans have the DNA mutation that researchers want to study. By checking this, researchers know what samples they are working with before starting their experiments.

If you would like to learn more about polymerase chain reaction, take a look at these resources by the Science Learning Hub and Your Geonome.

Snapshot written by Nola Begeja and edited by Larissa Nitschke

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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