Crispr Technology - The Potential Tool for Curing Huntington’s Disease

People with Huntington’s Disease (HD) are unable to control their movements, lose thinking ability, and have emotional problems. HD is a genetic disease caused by mutations in the Huntingtin Gene. DNA segments in the Huntingtin Gene are repeated abnormally higher in people with HD. There is currently no cure for HD. This is because the type of mutation varies, and the location of the mutation is in different parts of the gene (National Institute of Neurological Disorders and Stroke, 2020).

CRISPR: A Promising Tool for Treating Huntington's Disease

Researchers are testing Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR) technology to develop a treatment for HD. CRISPR is currently the most precise gene-editing tool available and involves ‘cutting and pasting’ sequences of Deoxyribonucleic Acid (DNA). Before CRISPR treatment for HD can be released to the public, extensive research and studies must be done to ensure that CRISPR is safe and effective (Doudna & Charpentier, 2014).

DNA is a macromolecule that carries the instructions for development, reproduction, and functioning of an organism. The DNA structure is a double helix, and each strand is made up of nucleotide molecules. DNA consists of four types of nitrogen bases: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C). The DNA’s instructions and its genetic code are determined by the sequence of these bases (Watson & Crick, 1953).

HD is an autosomal dominant disorder, which means that inheriting a single defective Huntingtin Gene is enough to cause the disorder. Every human inherits two copies of each gene, one copy is maternal, and the other is paternal. A parent with a defective Huntingtin Gene can pass on either the defective copy or the healthy copy. Therefore, there is a 50% chance of inheriting a defective Huntingtin Gene from a parent with HD. The defective Huntingtin Gene causes excessive build-up of the Huntingtin protein, which results in damage to nerve cells in regions of the brain. This causes Huntington’s Disease and hence hinders neurological function (Walker, 2007).

CRISPR technology utilizes a short RNA with a base sequence that is complementary to the desired DNA base sequence. This RNA is ‘loaded’ in Cas9, which is an enzyme able to cut the DNA at specific sites. CRISPR technology can be used in human cells, and it is possible to utilize this technology to treat genetic diseases such as HD by editing the faulty genes. Researchers at the Institute of Bioorganic Chemistry (IBC) in Poland utilized CRISPR Cas9 nickase. Instead of slicing both strands of the DNA double helix, nickase allowed just one of the strands to be sliced, which makes a much more precise gene edit (Zhang et al., 2015).

Researchers at IBC are hoping to open up new avenues into neurodegenerative research and rapidly move to human trials after the release of their new findings. The research team at IBC developed a new variant of CRISPR using Cas9 nickase, which is safer and more specific than the previous version. This makes it an “attractive treatment tool for Huntington’s disease” as “no sequence-specific side effects were observed” during the testing phase. This new CRISPR variant was successful in inactivating the mutant Huntingtin gene, ceasing the production of the toxic protein. Overall, the researchers were successful in editing the Huntingtin Gene, reducing approximately 70% of neurodegenerative proteins. As not all of this neurodegenerative protein was eliminated, the group must conduct further studies on cellular models of HD to ensure that the new variant of CRISPR is as effective and safe as possible before human trials can begin. However, CRISPR Cas9 nickase looks very promising, and it’s likely to replace its predecessor version (Smith et al., 2021).

Conclusion

In conclusion, scientists have been speculating about the potential of using genetic modification techniques such as CRISPR to treat genetic diseases ever since the technology was discovered. Scientists have been successful in using these techniques in vitro to eliminate diseases that cause mutations. Recently, China has begun using CRISPR technology in clinical trials to directly treat patients, and this is soon to begin in the U.S. However, genetic modification techniques have yet to be utilized in clinical trials to treat genetic diseases as complex as Huntington’s Disease (Cyranoski, 2016). The progress in CRISPR research continues to offer hope for future breakthroughs in treating not only HD but potentially other genetic disorders as well.

References:
- Cyranoski, D. (2016). CRISPR gene-editing tested in a person for the first time. Nature News.
- Doudna, J. A., & Charpentier, E. (2014). The new frontier of genome engineering with CRISPR-Cas9. Science, 346(6213), 1258096.
- National Institute of Neurological Disorders and Stroke. (2020). Huntington's Disease Information Page.
- Smith, J. D., et al. (2021). Advances in CRISPR technology for the treatment of Huntington’s Disease. Journal of Neurogenetics.
- Walker, F. O. (2007). Huntington's disease. The Lancet, 369(9557), 218-228.
- Watson, J. D., & Crick, F. H. C. (1953). Molecular structure of nucleic acids; a structure for deoxyribose nucleic acid. Nature, 171(4356), 737-738.
- Zhang, F., et al. (2015). CRISPR genome editing: Prototypes and perspectives. Cell, 163(1), 16-20.