New hope for saviour sibling cures

The world-first is hailed as a major breakthrough which could help speed up the development of cures for diseases such as Parkinson's and rare cancers.

The discovery that stem cells can be extracted when the embryo contains only four cells could improve doctors' ability to treat ill children through the creation of so-called "saviour siblings" to provide a stem cell transplant.

The discovery by Dr Hilde Van de Velde from Vrije Universiteit Brussel in Belgium could also overcome ethical objections by pro-life groups. The fertility expert said the finding reduces the number of embryos destroyed during screening for genetic diseases as four-cell embryos are more robust. She said: "By making it possible to intervene at an earlier stage and without destruction of the embryo, ethical concerns will be diminished."

Until now, scientists have only managed to extract stem cells from eight-cell embryos.