The Changing World Within Our Genes

Natalie Wing

ABSTRACT

We live during a time when we have tools to modify not only the world around us, but also ourselves—our own genes. But, how well do we truly know how to use such tools? How effectively can we put them to use? Since CRISPR and other gene editing therapies have been discovered, humans have been asking if we should embrace gene editing, but perhaps the more appropriate question to ask is if we can successfully use gene editing. Indeed, the potential benefits of CRISPR/Cas9 gene editing in treating patients of the medical community are manyfold, but the consequences of off-target effects are also a serious issue to consider.

INTRODUCTION

Genes are what make us, but now, we can make our genes. In this modern day and age, novel biotechnology allows us to edit our genomes, potentially removing deleterious mutations and curing diseases once thought incurable. Oftentimes, scientists and philosophers grapple with whether such procedures should be performed, but many tend to forget the question of whether such procedures can be completely successful. While techniques such as homologous directed repair CRISPR/Cas9 can indeed target and remove mutations, they have also been associated with serious off-target effects. ¹ Increasing the specificity of the guide RNA for CRISPR/Cas9 can significantly mitigate some of these off-target effects. However, it would also significantly decrease the effectiveness of gene therapy, making it more difficult to treat the disease itself. Such large tradeoffs between treating a particular disease and risking the creation of a worse illness in its place, contribute to some controversy regarding gene editing. Although gene therapy does seem to be an integral part of treating disease in the future, perhaps some present hesitance against using it is warranted.

Before we can discuss what policies should regulate gene therapy, we must first discuss the current policies in place. It is important to note that these policies vary from country to country. Mexico and China, for instance, are both lenient in their policies towards human germline modification—though in China, current policies are regulatory, whereas in Mexico, they are derived from legislative actions. ² The U.S. and England are neither particularly restrictive nor permissive towards germline genetic modifications, but Canada and Australia, for instance, have very restrictive laws against germline modifications. ² There is much less variation among country standpoints, however, when referring to somatic gene therapy. ² Indeed, most countries with the technology for gene therapy take a more intermediate standpoint (not particularly restrictive but not encouraging, either) towards somatic gene therapy. ²

THE TECHNICAL ISSUES

At this point, you may be wondering why researchers have not pushed harder against such regulations, and why most countries have decided to take a more intermediate rather than permissive approach to even somatic gene editing, where there is little concern for inducing social stratification or affecting human evolution. This is because, despite the numerous advances occurring daily in the field of CRISPR/Cas9 research, CRISPR still does not have the level of precision we desire of it. In a 2003 study of Arabidopsis thaliana modified with a single copy of transgene, for instance, 71% of the test plants had small mutations near the insertion site, including indels of 1-100bp, and the other 29% had large scale insertions, re-arrangements, duplications, and/or deletions. ¹ In a cystic fibrosis study where a gene regulating chlorine movement was inserted, a gene chip revealed that up to 5% of the monitored mRNA changed in quantity. ¹ Further, in another study, scientists inserted a gene into a group of test subjects with X-SCID. However, this insertion permanently turned on a nearby promoter controlling growth receptor LMO2, which increased T-cells, and led to leukemia ¹ While studies from the past few years, may have not shown as many off-target effects as before (implying CRISPR techniques have improved over time), such mutations still pose a “safety concern”, and other researchers have conceded that they “may occur at sites beyond those predicted.” ³

On the other hand, focusing on specificity to decrease off-target effects implies that CRISPR is not completely effective at correcting a genetic mutation across cells. Take, for instance, a 2016 muscular dystrophy study using CRISPR for exon excising, which showed that 34% of the resulting ligations were imprecise and 41% of resulting mRNA transcripts still included the exon of interest. ⁴ A more recent study attempted to completely remove a particular protein from the cell, but there was still 20% of wild-type levels of the protein in the cell after the experiment. ⁵

ACKNOWLEDGING THE POSSIBLE BENEFITS

Still, this is not to say there are not benefits to gene therapy, or that gene therapy cannot be used to improve quality of life in patients, even if it cannot completely cure them. Referring back to the aforementioned 2016 muscular dystrophy study, for instance, it is important to note that protein levels increasing to only 4% their wild-type levels “is sufficient to improve muscle function,” so the observed increase to 8% of wild-type protein levels, while not curing the disease entirely, would help improve patient mobility. ⁴ We must also note cases like Jack Kennedy, who was missing both copies of the RPE65 gene, and as a result, would go completely blind. However, CRISPER-Cas9 therapy helped restore some of his sight. ⁶ Ignoring the potential long-term effects and the fact that his sight was not completely restored, we can likewise conclude that gene therapy was a success for him.

CONCLUSION

But why rush into gene editing when more efficient techniques are still being designed? A recent article in Nature, for instance, analyzed the complex formed between CRISPR’s guide RNA and the DNA in our cells. It discovered a particular weakness in CRISPR’s RuvC domain allowing for mismatches to be stabilized (resulting in off-target effects). ⁷ Perhaps in a few more years, this too can be corrected, and we will not need to be as hesitant about gene editing as we currently are. It is true that we have advanced to the point where we can essentially make our genes, but just as the human race had to improve the engine before we took to the skies, we too, must improve CRISPR before diving full force into the age of gene therapies.

ABOUT THE AUTHOR

Natalie Wing is an associate editor at the Harvard Health Policy Review and a sophomore concentrating in Molecular and Cellular Biology with a secondary in Classics at Harvard College

REFERENCES

Smith JM. Genetic Roulette: The Documented Health Risks of Genetically Engineered Foods. 1st ed. Hartford, Vermont: Chelsea Green Publishing; 2007.

Isasi R, Kleiderman E, Knoppers BM. Editing policy to fit the genome?. Science. 2016 Jan 22;351(6271):337-9.
Long C, Amoasii L, Mireault AA, McAnally JR, Li H, Sanchez-Ortiz E, Bhattacharyya S, Shelton JM, Bassel-Duby R, Olson EN. Postnatal genome editing partially restores dystrophin expression in a mouse model of muscular dystrophy. Science. 2016 Jan 22;351(6271):400-3.
Nelson CE, Hakim CH, Ousterout DG, Thakore PI, Moreb EA, Rivera RM, Madhavan S, Pan X, Ran FA, Yan WX, Asokan A. In vivo genome editing improves muscle function in a mouse model of Duchenne muscular dystrophy. Science. 2016 Jan 22;351(6271):403-7.
Incontro S, Asensio CS, Nicoll RA. Dissecting the Role of Synaptic Proteins with CRISPR. Genome Editing in Neurosciences. 2017:51-62.
Egender J. Vol. 1, Unnatural Selection. Netflix; 2018.
Bravo JP, Liu MS, Hibshman GN, Dangerfield TL, Jung K, McCool RS, Johnson KA, Taylor DW. Structural basis for mismatch surveillance by CRISPR–Cas9. Nature. 2022 Mar;603(7900):343-7.