A group of US scientists and activists want the next level of gene-editing techniques banned.

The Centre for Genetics and Society (CGS) has joined with Friends of the Earth to issue a report ahead of a major international meeting in Washington to discuss the ethical and policy issues surrounding genetic modification of humans.

Their concern is centred on the modification of human sperm, eggs and embryos, which could create new DNA that is passed on through generations.

The technology and techniques could one day eliminate inherited diseases (of which there are many), but they have a growing set of vocal opponents.

“Like so many powerful new technologies, gene editing holds potential for both great benefit and great harm,” said an open letter published by the groups.

“The implementation of heritable human genetic modification — often referred to as the creation of ‘genetically modified humans’ or ‘designer babies’ — could irrevocably alter the nature of the human species and society.

“Gene editing may hold some promise for somatic gene therapy [such as treating impaired tissues in a fully formed person].

“”However, there is no medical justification for modifying human embryos or gametes in an effort to alter the genes of a future child.”

CGS executive director Marcy Darnovsky says engineering the genetic future of families would be “highly risky, medically unnecessary, and socially fraught”.

“There is no good reason to risk a future of genetics haves and have-nots, a world with new forms of inequality, discrimination and conflict,” she said.

The groups are opposed in particular to a technique called CRISPR/Cas9.

CRISPR/Cas9 allows researchers and scientists to manipulate genes just like the “find and replace” function in word processing.

Microscopic zinc fingers are used to slice and splice the genetic ‘tape’, by introducing enzymes that bind to genes.

This can include mutated genes that may be associated with a given condition or disease, allowing it to be replaced or repaired.

Advocates say CRISPR is the best chance at allowing scientists to prevent heritable diseases.

Opponents are worried that more widespread access and use would allow future parents to pay for genetic enhancements such as greater intelligence or athletic ability – like the movie ‘Gattaca’.

There is also a risk that unknown effects might come from the new genes being passed down through reproduction.

It is already becoming fairly common in the lab to use gene-editing techniques that alter the DNA of non-reproductive cells to repair diseased genes.

But the new objections mostly relate to so-called “germline editing” wherein reproductive cells are modified.

The US Government endorsed a ban on germline editing earlier this year, saying more study of the ethical issues is required.

Scientists led by one of the key developers of the CRISPR technique have similarly called for a voluntary research ban on using it for germline editing, saying concerns about safety and eugenics must be allayed first.

Chinese scientists have already reported carrying out the first experiment that altered the DNA of human embryos, though some speculate the science is further advanced than this, but has not been revealed to keep ethical concerns to a minimum.

Even so, the news made public was enough to ignite outcry from scientists, though some defend the Chinese research as employing caution and safety by using only non-viable human embryos.