By Michelle Yang
For genetic disorders such as sickle cell anemia or Huntington’s disease, doctors have often focused on how effectively patients’ symptoms can be managed. Recently, scientists have discovered how to address them at their root cause.
But what happens when we try to treat genetic mutations that don’t necessarily qualify as disorders? Even as we’re researching them, scientists still aren’t quite sure.
In Feb. 2025, researchers from Mie University in Japan developed a method for removing the third copy of chromosome 21, the structure responsible for causing Down syndrome, through the gene editing tool Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR). CRISPR allows scientists to pinpoint targets in DNA that may contain a mutation and remove them using an enzyme called Cas-9.
The use of CRISPR-based gene editing, which biochemist Dr. Jennifer Doudna pioneered in 2012, is “probably one of the top ten discoveries in human history, from a biomedical field,” according to Dr. Danith Ly, a professor of chemistry at Carnegie Mellon.
Down syndrome is the most common chromosomal form of intellectual and physical disability, resulting in large deficits in cognitive and motor development. If CRISPR can be applied in clinical use to treat Down syndrome, it could impact one in 691 people born.
Using CRISPR-based therapies to treat conditions such as Down syndrome, however, comes with a host of financial, ethical, and accessibility concerns.
For one, they are expensive. Casgevy, the only FDA-approved CRISPR therapy to treat sickle cell anemia, costs $2.2 million per patient. Lenmeldy, another gene therapy, is the most expensive drug in the United States, costing $4.25 million per patient.
The reason for these high costs, Dr. Ly explained, is due to the amount of funding required to go through clinical testing and use. Performing clinical trials may “cost anywhere from half a billion to a couple billion dollars” and take anywhere from five to 10 years on top of how long it takes for therapies to get approved for use.
The currently approved gene therapies work “ex vivo”, meaning they are given to blood cells outside of a person’s body that then circulate throughout their system. These genetic changes last as long as the blood cells are alive, making them impermanent.
However, the proposed therapy for Down syndrome takes place at the embryonic level, which means parents have to go through IVF for the procedure to take place. “And you come back to, ‘Who can afford this?’” says Dr. Stephanie Wong-Noonan, a professor of biology at Carnegie Mellon. “It’s going to be inaccessible unless there’s some way to support that, either through making it easier to produce the product, or providing some kind of government funding so that it doesn’t cost people so much.”
Embryonic changes also affect the genome itself — meaning that its revisions will affect all future generations. That means a mistake in the editing, “even a 0.1 percent difference, will not only change you in your lifetime, but your children down the road,” Dr. Ly said.
There’s also the question of the extent to which CRISPR-based treatments should be used. While not many therapies are approved now, Dr. Ly acknowledges that this “technology will eventually be perfected, and I think the more options we have, the better off we will be. The scientific community really embraces the idea, but we just don’t know.”
“If you can correct one thing, you can correct everything. And the question is always where you draw the line,” Dr. Wong-Noonan said. “What things will we correct? Or should we correct? There are lots of morally gray areas when it comes to these types of technologies.”
And maybe there’s not meant to be a clear answer. “CRISPR is never 100 percent, right, and understandably so. In evolution, there’s always a blurry line,” Dr. Ly said. “And maybe that’s a part of evolution. It’s designed to generate diversity as we progress through life.”