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Treating genetic disorders: Could gene editing help cure incurable diseases?

December 12, 2018

Gene editing could change how we treat diseases. But is everybody ready for it?

Little more than a half-century ago, very little was known about the genetic factors that contribute to human disease. The discovery of DNA in 1953 completely changed that. We learned that different sequences within our DNA dictate different characteristics and functions, and that sometimes there are mistakes in this DNA – mutations in genes that cause many different kinds of diseases.

In 2003, researchers announced that they had successfully sequenced the complete set of DNA in the human genome. From this base, we have been able to identify around 6,000 diseases1 that are caused by specific genetic mutations. Today, we can find a gene suspected of causing a disease in a matter of days, rather than years, while genetic testing on blood and other tissue is now available for over 2000 conditions2, both rare and common.

These discoveries have not only improved our understanding of diseases but also our approach to treating them. Scientists are developing cutting edge techniques that could potentially cure life threatening diseases, ones we considered incurable in the 20th century.

59% of people support the use of genome editing to cure a life-threatening disease

Gene genie

Today we are taking the first steps towards tackling genetic diseases at the root. Many of these techniques are still in their early stages, but each one of them holds remarkable promise.

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Gene therapy

Gene therapy involves introducing healthy genes into cells in order to correct a genetic disorder. There are several approaches to combating a defective gene – replacing it, deactivating it, or even introducing new functioning genes alongside the defective ones without editing the existing genomic material.

Gene therapy can take place either within or outside of the body. Ex vivo gene therapy works by isolating cells with a genetic defect from a patient, growing these cells in a culture, introducing the therapeutic gene to the cells and then transferring these into the body to help fight a disease. In vivo gene therapy, on the other hand, sees a functioning gene inserted into a carrier or vector (such as a non-replicating virus) and this is then injected directly into the blood stream.

These techniques could help patients circumvent the burden of genetic defects. For people with hemophilia, for example, life is an ongoing burden to manage their disease. The illness is caused by a deficiency in the genetics of the blood clotting protein factor VIII. Current treatments require the sufferer to make regular injections of factor VIII.

However, gene therapy may hold a more long-term answer. A potential treatment being developed by Bayer in collaboration with Ultragenyx, would work through the intravenous administration of the clotting factor VIII gene to hemophilia A patients via a non-pathogenic carrier virus targeting the patient’s liver. This would enable their bodies to then produce function factor VIII. The hope is to develop a long-term cure of the coagulation system via a single intravenous dose that would last 5-10 years.

"The greatest potential surely lies in using this technology to treat hereditary diseases, such as cystic fibrosis or sickle-cell anemia."

– Professor Emmanuelle Charpentier, co-creator of the CRISPR-Cas9 technique

Genome editing

While gene therapy has been researched for decades, genome editing is only at the beginning of its journey but has enormous potential. The techniques focus on precisely cutting out the defective genes and replacing them with the correct elements or just shutting down a special function causing a disease, a process known as knock-out.

There are a number of recognized genome editing techniques – directly engineering the cell nucleus, such as with CRISPR-Cas9; utilizing viral systems; and creating synthetic transposons, or ‘jumping genes’, that can change their position within a genome.

CRISPR-Cas9 is the most well-known of these methods. The technique acts like a pair of molecular scissors, enabling the DNA strand to be cut at precisely defined points – allowing scientists to repair genes with incredible accuracy.

“It’s comparable with swapping one word for another in a text on a computer. The greatest potential surely lies in using this technology to treat hereditary diseases, such as cystic fibrosis or sickle-cell anemia” states Professor Emmanuelle Charpentier, co-creator of the CRISPR-Cas9 technique.

But gene editing comes with controversy

Genome editing techniques are currently being developed to combat a wide variety of diseases from cancer to coronary heart disease and have the potential to transform the lives of millions of people.

However, these techniques remain controversial. While 59% of people support the use of genome editing3 to cure a life-threatening disease, there is plenty of concern about the risks of changing a person’s DNA.

This is particularly the case with germline editing – that is, edits to the part of the genome that are inherited by our children. In germline editing, you’re not just changing the genes of a single patient. You’re theoretically making permanent genetic edits to future generations.

This is why there is currently a moratorium on editing germline, or reproductive, cells and much of the focus on treatment is on editing somatic cells, the majority of our cells whose information cannot be passed from generation to generation.

The very nature of gene editing, of changing the DNA that makes us who we are, understandably creates concerns. But the more we learn about the defective genes that cause diseases, the more sense it makes to target these and create treatments that could potentially cure the previously incurable.

Footnotes

  1. Xiaoming, W. et al. Identification of Sequence Variants in Genetic Disease-Causing Genes Using Targeted Next-Generation Sequencing, Beijing Genomics Institute, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3244462/
  2. Genetic Testing: How it is Used for Healthcare, U.S. National Institutes of Health, https://report.nih.gov/nihfactsheets/ViewFactSheet.aspx?csid=43
  3. McCaughey, T. et al. A Global Social Media Survey of Attitudes to Human Genome Editing, Cell Stem Cell, https://www.sciencedirect.com/science/article/pii/S1934590916300546
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