The technique, invented by Jennifer A. Doudna of the University of California, Berkeley, and Emmanuelle Charpentier of Umea University in Sweden, known as Crispr-Cas9, "co-opts the natural immune system in which bacteria remember the DNA of the viruses that attack them so they are ready the next time those same invaders appear," according to the NYT article. "Researchers can simply prime the defense system with a guide sequence of their choice and it will destroy the matching DNA sequence in any genome presented to it."
However, the technique is not always precise and sometimes cuts the genome incorrectly. What this would mean in a clinical setting still needs to be studied further.
With an issue that raises many ethical questions, leading researchers are asking the scientific community, both in the U.S. and abroad, to hold off on human germline modification until safety is assessed and so that the public can understand the magnitude of implications.
The NYT interviewed David Baltimore, a former president of the California Institute of Technology and a member of the group whose paper on the subject was published in the journal Science. "You could exert control over human heredity with this technique, and that is why we are raising the issue," he told the NYT.
Altering the human germline would mean making changes to DNA that would pass on to the next generation, not just diseases, but things like physical traits and intelligence. Although technology has reached the point where this can be done, there is still a question of if it should be done.