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New genetic treatments can help couples ensure their baby will not inherit family diseases such as cancer but, as Adam Wishart explains, advances in science bring with them new dilemmas.

A year ago, in South Shields, teacher Daniel Stanley faced one of the toughest things for a brother - watching his younger sister Natasha die of breast cancer at the tender age of 28.

"It is hard to watch someone like that. Optimistic one minute, and then to receive another diagnosis," said Daniel.

As Natasha died, she discovered that the cancer had a genetic basis on one of two breast cancer genes, BRCA1 and BRCA2.

Daniel was also tested and found out that he had the same gene.

It placed him on the horns of a very difficult dilemma because he wanted children, but did not want to pass on the gene.

Through his genetic counsellors, he and his partner Danielle were offered Pre-Implantation Genetic Diagnosis (PGD) - a technique which screens IVF embryos for genetic disorders.

When the embryos are only eight cells large, an embryologist very carefully makes a hole in each shell, and sucks out a single cell to be tested genetically.

Any that are free of the faulty gene are transferred into the mother's womb.

PGD has been offered by the NHS for more than a decade for serious diseases that come early in childhood, like cystic fibrosis or Tay Sachs, a neurological disease.

But for a treatable adult disease the ethics are debatable, and so the first child free of the breast cancer gene by PGD was born only in 2009.

There are some that argue that by using PGD for these diseases Britain is taking a step onto a dangerous slippery slope.

Professor Michael Baum, a leading researcher in breast cancer, is doubtful whether PGD should be used for inherited breast cancer.

"There is a phenomena in genetics and cellular development called co-expression in which two genes can be stuck together," he said.

"If you have the mutant gene, that might be co-expressed with favourable components of the human genome.

"So if you breed out the BRCA1 and BRCA2 mutation you may inadvertently breed out something of value.

"Just say it is the gene or the complex of genes for beauty, or say it is a complex of genes for high intelligence.

"There is a risk. If we select out all the embryos that have these mutations then we might be selecting out some of the best people in society.

"Now you think that is facetious. It may not be beauty and intelligence but it may be something else that has an evolutionary advantage."

Pioneers

Despite the arguments, Daniel and Danielle have decided to become part of the pioneers for breast cancer.

"I think I'd feel a lot less comfortable with the idea if we were being more selective - if we were saying we wanted a boy or a girl," said Daniel.

Danielle said: "We are not changing the genes, we are just selecting the embryos without a cancer gene.

"The other option we were given was to conceive naturally and then to have a gender test and then have a termination if it was a girl. I couldn't do that."

Daniel feels that having watched his sister, preventing that kind of suffering is almost a kind of duty.

"If science has given me that power to do something about it then really I should use that power. That is something that the human race has created - it is part of the history of our progress and that is an opportunity really."

Daniel and Danielle hope to go through PGD later in the year at Guy's hospital in London.

Should I Test My Genes? The Price of Life will be on ³ÉÈË¿ìÊÖ Two at 2100 BST on Tuesday 5 July 2011 and after on ³ÉÈË¿ìÊÖ iPlayer (UK only)