CRISPR is a groundbreaking technology that enables researchers to precisely locate and modify specific segments of DNA within a cell’s vast genome. Since the discovery of CRISPR-Cas9 genome editing in 2012,1 this tool has revolutionized biomedical research, allowing scientists to investigate the biological functions of genes and the impact of genetic mutations in disease. Today, CRISPR’s applications have expanded beyond research into therapeutics, diagnostics, and more.
In the context of ALS research, CRISPR is being used to study the genetic mutations associated with the disease, offering insights that could lead to new therapeutic approaches. The potential of CRISPR-based therapies is particularly exciting, as they hold the promise of permanently correcting genetic mutations, potentially leading to innovative treatments for various genetic disorders, including ALS.
To accelerate innovation in this space, Target ALS launched an open call for proposals through its New Modalities Consortia in late 2024. This initiative aims to support the development of novel therapeutic approaches, including gene editing technologies like CRISPR, to drive progress in ALS treatment. By fostering collaboration between academic researchers and industry leaders, Target ALS is helping to bridge the gap between scientific discovery and clinical application, ultimately bringing new hope to those affected by ALS.
What is CRISPR?
Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) refers to a technology used to remove, add, or otherwise alter a genome. CRISPR has become a promising gene editing system because of its accuracy, efficiency, and cost.
CRISPR-Cas9 (often referred to simply as CRISPR) technology is adapted from the natural immune systems of bacteria. When bacteria are infected with a virus, they incorporate pieces of the virus’ DNA into their own. These DNA segments are known as CRISPR arrays, which provide the bacteria with a memory of the infection and allow them to recognize the virus in the future. If the virus attacks again, the bacteria can produce the matching RNA segments from the CRISPR arrays. These segments attach themselves to the virus’ DNA and use an enzyme called Cas9 to disable the virus by cutting its DNA apart.2 After this discovery, researchers realized that the CRISPR RNAs could be programmed for targeting Cas9 to any DNA sequence simply by using guide RNA (gRNA), a specific RNA sequence that recognizes the target DNA region of interest. Adaptations of the core CRISPR technology make it possible to activate, silence or otherwise manipulate the target genes.
CRISPR technology is currently being investigated in the hopes that it can edit genetic mutations that lead to several different types of diseases, including neurodegenerative diseases like ALS. The technology has also helped elucidate some of the molecular mechanisms that play a role in the development of these diseases.3
How has CRISPR technology impacted ALS research?
CRISPR/Cas9 technology has forwarded research in ALS by enabling study of disease-related genes in preclinical models. There are roughly 40 genes which can have mutations associated with ALS risk, with the SOD1, FUS, C9orf72, and TARDBP genes being the most common. CRISPR can be employed to target these genes and replace the mutated DNA sequences that lead to protein misfolding and aggregation and other aspects of ALS pathology.4 Such an approach can be conducted in cultured cells or mouse models.4
Recently, Target ALS-funded researchers found that CRISPR can be used to excise the hexanucleotide repeat expansion (HRE) mutation in the C9ORF72 gene in a variety of preclinical models.5 This work has exciting therapeutic implications since the CRISPR-edited cells lacking the C9ORF72 HRE have reduced amounts of RNA foci and fewer toxic poly-dipeptides, two major pathological hallmarks of C9-ALS/FTD. Another study in 2018, funded by Target ALS utilized CRISPR/Cas9 to investigate the role of TP73 in ALS disease biology. Researchers used CRISPR/Cas9 to delete wild-type TP73 in zebrafish and found motor neuron defects consistent with motor neuron degeneration that stems from rare TP73 gene mutations found in ALS patients.
CRISPR can also be used in the design of high throughput screens to test the function of hundreds of genes simultaneously. Screens can be designed as arrays or pooled-CRISPR screens.7 Arrayed CRISPR screens involve targeting each gene with a specific gRNA in individual wells of a multi-well plate. In a typical pooled CRISPR screen, a CRISPR guide RNA (gRNA) library is introduced in bulk into cells, such that individual cells receive many different gRNAs and are perturbed according to the gRNA received by the cell. In 2022, Target ALS funded two new consortia utilizing CRISPR-based screens to gain deeper insights into the complex molecular mechanisms underlying the disease.
Are there CRISPR-based therapeutics for ALS?
Although there are currently no approved CRISPR therapeutics for ALS, several research groups and biotech companies are actively working to develop gene-editing treatments for the disease. Scribe Therapeutics, co-founded by CRISPR pioneer and Nobel Prize winner Dr. Jennifer Doudna, announced a $400 million research collaboration with Biogen to develop CRISPR-based therapeutics for ALS. CRISPR Therapeutics, co-founded by Target ALS and Dr. Emmanuelle Charpentier—another Nobel laureate for her work on CRISPR—is collaborating with Capsida Biotherapeutics to develop gene-editing therapies for ALS. These companies are currently in the preclinical stage of development, exploring promising approaches to modify or correct disease-causing genetic mutations.
Target ALS is also actively supporting gene-editing research as part of its commitment to accelerating therapeutic development. One of the most studied genetic mutations in ALS occurs in the C9orf72 gene, which is responsible for around 10% of all ALS cases. This mutation is caused by a repeat expansion—an abnormal repetition of a DNA sequence that disrupts the gene’s normal function. When the mutated gene is transcribed, the repeat expansion leads to the production of aberrant, potentially toxic proteins and RNA strands that can contribute to motor neuron degeneration.
Early clinical trials targeting the C9orf72 mutation have primarily focused on the “sense” RNA strand, but researchers are now exploring whether targeting the antisense RNA strand could also be an effective therapeutic strategy. Target ALS is funding multiple approaches to address this challenge, including gene editing with CRISPR, Zinc Finger Nuclease, disiRNA, and antisense oligonucleotides (ASOs).
Among the funded researchers, Dr. Claire Clelland of UCSF is pioneering the use of CRISPR to remove the entire disease-causing repeated DNA sequence in the C9orf72 gene. This work represents a potentially groundbreaking therapeutic approach, targeting the root cause of familial ALS at the DNA level. Additionally, CRISPR Therapeutics and researchers at the University of Florida were awarded a Target ALS grant to develop CRISPR-Cas9-based approaches for ALS, further advancing the field of gene-editing research for the disease.
Meanwhile, companies like Ionis Pharmaceuticals and Atalanta Therapeutics are advancing treatments that target the antisense RNA strand using ASOs and disiRNA—small molecules that bind to RNA and prevent the formation of toxic proteins. Kathy Morelli, a Target ALS Springboard Fellow who recently opened her own lab at University of Vermont, is targeting the sense and antisense RNA strands from C9orf72 using a targeted degradation technique similar to CRISPR called zinc finger nucleases.
These efforts, supported by both biotech innovators and funding from Target ALS, highlight the immense potential of CRISPR and related gene-editing technologies in reshaping the future of ALS treatment. While these therapies are still in development, they represent a critical step toward the possibility of a long-term, disease-modifying treatment.
Will CRISPR Technology be able to help cure other diseases?
Currently, there are no CRISPR cures for any disease, but research continues to expand, offering hope for the future. Thanks to increased funding and global collaboration, CRISPR-based treatments are being explored for a wide range of conditions—including HIV, high cholesterol, and neurodegenerative diseases like ALS.
The first CRISPR cure will likely target a condition caused by a single-gene mutation, as these provide clearer therapeutic targets. Sickle-cell disease, one of the most common genetic conditions worldwide, is a leading candidate. Early clinical trials using CRISPR–Cas9 have shown promising results for both sickle-cell disease and beta-thalassemia, suggesting that CRISPR could provide long-term solutions for genetic blood disorders.
CRISPR is also being investigated for its potential to treat certain cancers, autism, muscular dystrophy, and inherited eye disorders. In neurodegenerative research, scientists have used CRISPR to identify and modify genes linked to Alzheimer’s and Huntington’s disease, with some success in reducing harmful protein accumulation in lab models.
For ALS, CRISPR is being used to study and target genes known to contribute to the disease, such as SOD1 and C9orf72. Researchers are exploring how CRISPR might help correct mutations that drive ALS progression, potentially paving the way for future gene-editing therapies. While these treatments are still in the early stages, they offer a glimpse into how CRISPR could one day change the outlook for ALS and other neurodegenerative diseases.
What are the limitations of CRISPR-based therapeutics?
A major concern for implementing CRISPR/Cas9 for gene therapy is the relatively high frequency of off-target effects, genes that are edited by Cas9 that weren’t originally intended to be targeted.10 In addition to technical limitations, CRISPR/Cas9, like traditional gene therapy, still raises concerns for immunogenic toxicity, or an immune system reaction that could create undesirable side effects of the therapy.
Frequently Asked Questions
What are the Advantages of CRISPR Technology?
The CRISPR-Cas9 system is more accurate, efficient, and inexpensive than other gene therapies. It is also more straightforward and versatile than other techniques used to alter genes. For example, targeting and modifying the C9orf72 repeat expansion at the DNA level with other gene editing technologies is more difficult or impossible.
Why is CRISPR So Powerful?
CRISPR is a powerful gene editing technology because it can directly target genes and very specific DNA mutations in humans, animals, and plants. CRISPR is being used to test the function of hundreds of genes simultaneously in high-throughput screens with ALS models.
Is CRISPR Considered DNA or RNA Technology?
Initially, CRISPR was considered a DNA technology because it targets a specific family of DNA sequences. However, more recently, researchers discovered that a subset of Cas enzymes could also act on RNA sequences.
Will CRISPR Technology Be Able to Help Cure Other Diseases?
In theory, CRISPR has the ability to treat or cure any disease caused by an identifiable genetic mutation. However, many diseases are multifactorial and have environmental components. It’s unclear to what extent CRISPR alone can truly cure complex diseases.
How Does CRISPR Compare to Gene Therapy?
Gene therapy refers to a group of technologies that can insert a functional gene in place of a mutated gene. There are multiple tools researchers can use to edit genes, and CRISPR is one of them. Simply put, CRISPR/Cas9 refers to a specific method of altering DNA for gene therapy.
Other gene editing methods include zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs).12
Sources:
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2. Questions and answers about CRISPR. The Broad Institute. Retrieved, December 14, 2022., from https://www.broadinstitute.org/what-broad/areas-focus/project-spotlight/questions-and-answers-about-crispr
3. Zhu X, et al. (2021, 14 Jun). Gene therapy for neurodegenerative disease: clinical potential and directions. Frontiers in Molecular Neuroscience. https://www.frontiersin.org/articles/10.3389/fnmol.2021.618171/full
4. Kramer, N.J, et al. (2018, 24 Jun). CRISPR–Cas9 screens in human cells and primary neurons identify modifiers of C9ORF72 dipeptide-repeat-protein toxicity. Nature Genetics. https://www.nature.com/articles/s41588-018-0070-7
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