But there is also the prospect of avoiding heritable, genetic diseases that can handicap or kill.
Congress has enacted barriers to clinical trials for such genetic trials, and the National Institutes of Health has banned funding. The UK received a licence in 2016 to carry out CRISPR on human embryos for research into early development.
Beyond medicine, researchers are also using gene editing technology in a wide range of applications including improving crop growth, hatching malaria-resistant mosquitos and growing algae that produce biofuels. They effectively corrected the problematic sperm gene 72 per cent of the time, and even in those instances where they did not correct it, the problematic gene was still deleted. While Chinese researchers have conducted three CRISPR trials on human embryos, the OHSU study was by far the largest procedure with the most embryos.
Genetics and ethics experts not involved in the work say it's a critical first step - but just one step - toward eventually testing the process in pregnancy, something now prohibited by US policy.
In the other corner is Chinese-born American Feng Zhang of the Broad Institute in MA, who used CRISPR in 2013 to alter cells with a nucleus (eucaryotes) found in plants, animals and humans.
News of the remarkable experiment began to circulate last week, but details became public Wednesday with a paper in the journal Nature.
"There is a long road ahead, particularly if you want to do this study in a regulated way". This time the researchers used normal embryos, which they found increased the proportion of embryos that were edited from 14% to 50%. It's well known among cardiologists for killing young athletes.
Those results raised concerns that any effort to manipulate genes in a human embryo could lead to unintended edits in other genes - known as "off-target effects" - or could lead to embryos containing a mixture of cells with corrected genes and cells with uncorrected genes, a problem known as "mosaicism" that could end up failing to prevent disease. The embryos were created from eggs donated by healthy women, which were artificially inseminated with sperm from males carrying the mutation.
It is the first time the powerful gene-editing tool Crispr-Cas9 has been used to fix a mutation responsible for a common inherited disease.
"It was easy", Mitalipov said.
Unfortunately, this process isn't very efficient in adult cells in which CRISPR has been tested, so Mitalipov expected similarly low yields in the embryos.
The Salk scientists and their colleagues say they never meant to implant any of the embryos used in their research, much less to bring any of those embryos to term. The US study destroyed the embryos after just a few days and the work remains at an experimental stage.
Speculation swirled after reports came out last week that a group of US scientists had CRISPR'd human embryos for the first time. They were not intended for implantation either. "But I think that's possible to do".
The research raises obvious concerns around the ethics of genetic engineering.
"It is a very important study", said Dr. Dusanka Babovic-Vuksanovic, genomics chair at Mayo Clinic in Rochester, Minnesota.
Mitalipov added that he believes it's "unlikely" that the technique would be used for genetic modification.
But the researchers say that method is expensive and hard on a mother.
She knows there's no hope for a genetic fix for her daughter, but she would like her son to be able to have children who are free of Batten's disease.
Currently, the most reliable way of screening for such inherited defects is by using IVF, screening the resulting embryos for the mutation and transferring only those without the mutation for pregnancy.
Oregon Health and Science University (OHSU) collaborated on the project with the Salk Institute and Korea's Institute for Basic Science. Embryos can be genetically screened before they are implanted during in vitro fertilization.
The key to the current success appears to come down to when the CRISPR editor is introduced to the embryo. "It's a staggering result", says geneticist Leanne Dibbens, at the University of South Australia. Theoretically, such technology could be used to help parents with a genetic disease or who are carriers of a genetic disease to undergoing selective manipulations of embryos prior to being implanted in the uterus. "This brings it closer to clinic, but there's still a lot of work to do".
"Regular clinics are not equipped and don't have the expertise to do it", he said.
The scientists said the procedure was surprisingly effective and that clinical trials could eventually be considered.