A group of biologists have called for a worldwide ban on the use of a gene editing technique that could alter human DNA across generations. They fear the technique may lead to unsafe or unethical uses.

The researchers said in a letter published in the journal Science on Thursday that the technique could be used to cure genetic diseases and defects, but could also be applied to enhance human genetic traits, which raised serious ethical concerns. “You could exert control over human heredity with this technique, and that is why we are raising the issue,” David Baltimore, a former president of the California Institute of Technology and one of the authors of the letter, told the New York Times.

Baltimore and 17 other scientists published the letter to the scientific community urging caution in using the technique. “Given the speed with which the genome engineering field is evolving, our group concluded that there is an urgent need for open discussion of the merits and risks of human genome modification by a broad cohort of scientists, clinicians, social scientists, the general public and relevant public entities and interest groups,” they wrote, calling for a ban on attempts to create genetically altered humans before the technique is fully understood.

The technology is a variant of Clustered Regularly Interspaced Short Palindromic Repeats, known as Crispr/Cas9, which exploits a mechanism of the body’s existing immune system whereby cells “remember” the DNA of attacking viruses to destroy them more easily. Researchers can activate the defense mechanism to recognize a sequence of their choosing, after which any matching sequences will be automatically edited out.

Crispr/Cas9 was recently used by scientists at the Salk Institute in California to remove HIV from infected cells, and to create monkeys with customized mutations. Since then, researchers have been using the technique to alter the DNA of human embryos, eggs and sperm cells, hoping to make the technology applicable at in vitro fertilization clinics.

The method acts as a universal search-and-replace function, effectively capable of altering entire genomes and, more significantly, being passed on to future generations. “It raises the most fundamental of issues about how we are going to view our humanity in the future and whether we are going to take the dramatic step of modifying our own germline and in a sense take control of our genetic destiny, which raises enormous peril for humanity,” George Daley, a stem cell expert at Boston Children’s Hospital and a member of the group, told the Times.

One of the ethical concerns involves the lack of knowledge of the genome as a whole. Researchers said the attempts toward altering a defective gene and replacing it with a normal one may end up being more harmful. “We worry about people making changes without the knowledge of what those changes mean in terms of the overall genome,” Baltimore reportedly said. “I personally think we are just not smart enough — and won’t be for a very long time — to feel comfortable about the consequences of changing heredity, even in a single individual.”

Many countries already ban “germline” genetic engineering -- which would change genes in ways that are heritable across generations -- citing ethical and safety concerns. However, some countries have poor regulation or none at all. Baltimore reportedly said the proposed ban was designed to “keep people from doing anything crazy.”

Last week, another group called for a global ban on germline editing, which would stop even research studies to understand the technique being pursued. However, their stand has been disputed by the authors of Thursday’s letter on the grounds that germline engineering could have applications in the future, once it is better understood.

Paul Berg, professor emeritus at the Stanford School of Medicine and one of the signatories of the letter, told MIT Technology Review that efforts to better understand Crispr/Cas9 should continue. “Science should not be impeded in its earliest stages by concerns that improvements in, and validations of, certain parts of the technology are opening the door to eugenics,” he said.