The International Society for Stem Cell Research (ISSCR) is calling for a halt to editing of the human germline genome until a larger discussion can be held among scientists and the public concerning ethical questions.

Editing of DNA is becoming easier, faster and less expensive than ever before. Changes can be made in the genetic code both in adults and embryos.

Clustered regularly interspaced short palindromic repeats (Crispr)-Cas9 is a fast, simple genome engineering method that could make editing DNA commonplace. Such a development could prevent genetic diseases and disorders, but could also be used to custom design babies.

Germline cells are those which are differentiated to a degree great enough that they pass their characteristics onto their offspring, usually by sexual reproduction.

"Thus, it is now possible to carry out genome modification in fertilized animal eggs or embryos, thereby altering the genetic makeup of every differentiated cell in an organism and so ensuring that the changes will be passed on to the organism's progeny," researchers wrote in a paper announcing their study.

Jennifer Doudna from the University of California, Berkeley, one of the leaders in Crispr-Cas9 techniques, was a prime author of the paper urging the moratorium. She was joined by David Baltimore, a Nobel Laureate biologist who was once president of the California Institute of Technology.

The new paper warns of a possible "slippery slope" of utilizing germline genetic modification, which could lead to unexpected results.

"[C]onsensus is lacking on what, if any, therapeutic applications of germ line genome modification might be permissible.  For example, some argue that the ability to eradicate disease justifies attempts at therapeutic editing of the human germ line, while others emphasize the difficulty of drawing clear distinctions between applications in human disease and attempts at human enhancement," the ISSCR stated in the report.

According to the authors, scientists do not have a thorough understanding of the safety or long-term effects of the gene editing technique.

However, the group does not take a position on the development of mitochondrial replacement therapy, in which the energy centers of egg cells are replaced with healthy versions of the organelle. Mitochondria are found outside the nucleus of cells, and replacement does not affect nuclear DNA, unlike human germline genome modification.

Many countries already ban any DNA editing which can be passed from one generation to the next. The United States has established regulations that would hold back such developments from being realized for years or decades. However, laws in some nations could allow for the creation of "designer babies" in the near future, driving the authors to call for a moratorium on research from scientists.

The letter urging a halt to Crispr-Cas9 and other human germline genome techniques was published in the journal Science.

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