Rewriting human DNA: The evolution of engineering genes

CRISPR is a genetic cut and paste tool, say Sanford genetic counselors

Genetic counselor Bethany Tucker holds a file folder while discussing the gene-editing tool CRISPR with a colleague in a genetics lab. Another colleague sits at a lab bench, facing away from the camera.

Humans have always been really good at engineering the world to best suit our needs. From breeding animals to cross pollinating plants, our ancestors were selecting for desirable traits without understanding the underlying genetics.

This process ensured animals and crops were stronger, more adaptable and more productive. Though not in a lab like modern day science, these were the earliest days of humans taking advantage of genetic principles.

Now, we have advanced so much farther. And, rather than just looking at everything around us, we are also looking within.

Learn more: Exploring Genetics series at Sanford Health

Scientists and researchers are on the brink of being able to rewrite the human genome. This offers incredible possibilities for the future, like treating — or potentially preventing — a life-threatening condition or disease.

Yet, there are still many questions and unknowns. Certified genetic counselors Dylan Platt, M.S., and Bethany Tucker, M.S., explain the capabilities and challenges being considered by the medical and scientific community in regards to human DNA editing.

CRISPR: Understanding human genome editing

“The genome is the complete set of genetic material — or DNA — in our cells, and human genome editing is a technique used to change a part of this DNA,” Tucker said.

CRISPR, or Clustered Regularly Interspaced Short Palindromic Repeats, is essentially a genetic cut and paste tool.

Platt said, “The information that makes each of us unique, and can cause disease, is written in the language of DNA. The technologies that edit a person’s genome are actually changing the spelling and/or wording of that genetic language by editing the DNA.”

“Just like editing software can search for particular words and replace them in a written document,” Tucker said, “CRISPR searches for a particular section of the genome to cut and replace.”

“It is a two-part protein complex,” Platt added. “So, one protein acts as a bloodhound, searching the genome for the correct area to edit. The other protein acts as a pair of scissors to cut out that specific area of DNA.”

Once an area has been cut out, the body’s natural DNA repair system takes over to correct the spelling mistake on its own. However, this process is far from perfect.

While this is revolutionary, genome editing is actually nothing new. It is a process bacteria have been using for billions of years to identify viruses the bacteria had previously encountered. However, in 2012, two scientists — Jennifer Doudna, Ph.D., and Emmanuelle Charpentier, Ph.D. — discovered its potential to be so much more, repurposing this ancient technology for use in the modern era.

The future of health and disease prevention

“Using this type of technology to treat and address severe health conditions is a natural step in the human story in regards to genomic medicine,” Platt said. “However, to ensure that progress is ethically made, discussions that include people with diverse backgrounds and opinions will be needed.”

Tucker asked, “What types of changes should be allowed? Who gets to decide this? How do we get permission to permanently change an individual’s DNA? The possibility to significantly impact health care exists, but challenges remain. This is one reason for the careful analysis and regulations of clinical trials.”

Today, U.S. clinical trials are determining if human genome editing can safely and effectively treat genetic conditions. However, human DNA editing could theoretically be used for other reasons, like changing physical traits or making other medically unnecessary changes. This fact is where people often, understandably, become concerned or question using a tool like CRISPR.

Looking at the challenges

“In current CRISPR clinical trials, scientists are only targeting cells in adults,” Tucker said. “They avoid rewriting DNA in cells that could be passed on to future generations. But, if scientists alter the cells of an embryo at the time of conception, every cell in that individual would have the genetic change, and this genetic change could be passed down to future generations.”

This is just one of the many challenges surrounding genetic editing technologies. Others include:

  • Accessibility: Although CRISPR is the cheapest and most promising type of genome editing tool, there will likely be a cost barrier to access.
  • Accuracy: Because genome editing is changing human DNA, it is extremely important that the correct area is edited. There is the possibility of editing the incorrect area of the genome because CRISPR is searching for repetitive sections of DNA.
  • Determining what to treat: Many genetic conditions have no treatments and ultimately will lead to a premature death. However, many other genetic conditions already have treatment, do not require treatment or are not considered a disability by members of that community. The question is where do we draw the line for what to treat and what to leave alone.
  • Unexpected genetic changes: While unintentional, there is the potential for scientists to accidentally create a new, unexpected problem within the genome.
  • What types of cells should be edited: This concern centers around the question of whether human genome editing should be used to treat or prevent genetic conditions. Treatment for a genetic condition would target cells that cannot be passed on. On the other hand, the edits needed to prevent a genetic condition would have the ability to be passed on to future generations.

While many challenges exist and are important for our society to discuss, one thing remains certain: The scientific and medical community is using clinical trials to ensure both safety and effectiveness before openly using human genome editing. Through this research and a deeper understanding of human genome editing, we may one day be able to responsibly and ethically affect the lives of many.

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Posted In Genetics, Research

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