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Human embryos have been genetically modified so that any changes made will be carried on into future generations for the first time, according to scientists.

Researchers around the world are bracing themselves for the results of a study by scientists in China that has introduced DNA changes to reproductive cells.

Although the scientific paper is yet to be published, the scientific world is abuzz with rumours that the work has been carried out.

Human embryos, like the one above, may have been genetically modified with new gene editing techniques

Many scientists have already reacted with horror at the idea, for fear it could be misused to allow parents to 'select' the genes they will pass on to their grandchildren.

They say that even embryos created in this way for research purposes only could have serious ethical and safety implications. They have described it as 'dangerous and ethically unacceptable'.

However, others argue that the technology could also be used to rid families of devastating inherited diseases like cystic fibrosis or certain cancers.

According to a report by the National Post, Professor George Church, a geneticist at Harvard Medical School, says a paper outlining the technology is due to be published.

He said: 'There is a paper from China. I don't think it's been accepted yet, but I think it will be at some point.'

His comments match those made by several leading scientists working with non-reproductive stem cells who have raised concerns over the new technology.

Until now scientists have concentrated on using genome editing techniques on somatic cells - non-reproductive cells like those found in skin, muscle, nerves, bone and liver for example - to help them study diseases.

Modifying the DNA of human embryos so that DNA changes are preserved in the germline - the sperm and eggs - means such alterations can be passed on to future generations.

Such work is already illegal in many countries around the world including the UK, but is permitted in the US and China.

A number of groups around the world are thought to be working on techniques to genetically modify human embryos.

Germ line genetic editing alters the DNA in sperm and egg cells - meaning the changes can be passed on

Xingxu Huang, from Shanghai Tech University in China has been seeking permission to perform the technique on discarded human embryos after having successfully using it to modify monkey embryos that developed into live animals.

Professor Church's own group is also said to be developing techniques that could be used to modify human embryos.

Dr Luhan Yang, a scientist with Church's group, recently outlined proposals to edit the human germline in an interview with Technology Review.

She proposed using immature egg cells from the ovaries taken from women undergoing surgery for ovarian cancer.

The immature egg would be grown and coaxed into dividing before a gene-editing technique known as CRISPR would be used to correct the genetic fault that was causing the ovarian cancer.

However, the project is not thought to be underway yet and it is not known if it has been approved.

Dr Yang, however, has been reported to have been involved in a similar project in China. 

Last month a leading group of biologists called for a worldwide moratorium on germ line research amid rumours that it had already been used to alter human embryos in China.

Edward Lanphier, chairman of the Alliance for Regenerative Medicine in Washington DC, and four colleagues, wrote in the journal Nature that such research could harm other areas of science by provoking a public outcry. 

They wrote: 'It is thought that studies involving the use of genome-editing tools to modify the DNA of human embryos will be published shortly

'In our view, genome editing in human embryos using current technologies could have unpredictable effects on future generations. 

Many scientists have already reacted with horror at the idea, for fear it could be misused to allow parents to 'select' the genes they will pass on to their grandchildren 

'This makes it dangerous and ethically unacceptable.

'Such research could be exploited for non-therapeutic modifications.

'We are concerned that a public outcry about such an ethical breach could hinder a promising area of therapeutic development, namely making genetic changes that cannot be inherited.

'At this early stage, scientists should agree not to modify the DNA of human reproductive cells.'

Their fears tap into concerns that such technology could be used to create 'designer families' where certain traits are selected for.

In reality such selection can be difficult as often there is no single gene that provides a single trait and many genes have multiple functions.