What’s the procedure that promises to deliver babies unaffected by the genetic abnormalities of their parents? It’s called heritable genome editing (HE) or germline editing and uses “gene editing” technology.
Currently, the fastest, cheapest and most reliable technique to edit genes is the CRISPR-Cas9 system.
Think of CRISPR-Cas9 system as pair of molecular scissors that has been programmed to edit a specific portion of DNA. Cas9 is a protein that can cut double-stranded DNA. It is coupled with an RNA sequence programmed to find the DNA sequence to be edited. When that target DNA is found, Cas9 binds to the DNA and cuts it, which shuts off the targeted gene.
CRISPR
The ability to use CRISPR for gene editing has changed the way scientists approach the treatment of diseases caused by changes in a single gene. But it’s important to distinguish between two types of gene editing: somatic gene editing and heritable gene editing.
Somatic gene editing affects only certain cells in a person in a way that does not impact reproductive cells. For example, a 36-year-old patient, Victoria Gray, suffering from sickle cell disease has had cells drawn from her bone marrow. Those cells were treated using CRISPR and then infused back into the patient. These edited cells produced a protein that helped alleviate the symptoms of sickle cell and improved the patient’s quality of life. But these changes would not be passed down to any child she subsequently had.
Victoria Gray, who has sickle cell disease, volunteered for one of the most anticipated medical experiments in decades: the first attempt to use the gene-editing technique CRISPR to treat a genetic disorder in the United States. Meredith Rizzo/NPR
In contrast, heritable genome editing (HGE) is the process by which human reproductive cells (sperm, egg cells) or embryos are “edited” with the goal to produce children. These changes in the genetic make-up of reproductive cells are passed down from generation to generation.
However, HGE carries safety risks and raises ethical questions, what some have called the “dark side of CRISPR”.
From a safety standpoint, the editing can cause unintended changes, such as the loss of an entire chromosome or big portions of it, which can doom the life of any child born with such edits.
Also, the use of HGE elicits ethical questions about the value of human life. It can cut people with disabilities out of existence—at the embryonic stage—without the rest of humanity even noticing. Although society at large may view genetic “perfection” as an undeniable good, many people with disabilities (for example several in the hearing-impaired community) are very protective of their genetic differences. Each human is intrinsically worthy of life just as he or she is.
In addition, the future child who possesses edited genes will have a genome to which he or she has not consented. Even with technological refinements to minimize unintended gene edits, do parents have the right to decide the genetic make-up of their future children and grandchildren?
From a regulatory standpoint, who would decide which genes are worth keeping and which ones should be removed from the human pool? “Society at large”? Agencies like the FDA? Scientists? Doctors?
At the moment, HGE is illegal throughout the world. But this regulatory prohibition has not stopped a scientist from experimenting on embryos using CRISPR. Twin babies, Lulu and Nana, were born from that experiment.
More about Lulu and Nana next…