Flaws in cloning procedure

Scientists have found more evidence that cloned animals tend to have genetic defects which cause them to have abnormalities or low survival rates, supporting the suggestion that human reproductive cloning would not be viable.

Rudolf Jaenisch and his team, from the Whitehead Centre for Biomedical Research in Massachusetts, US, studied the genetic make-up of the liver and placenta in cloned mice. They found that as many as one in 25 of the genes in the placenta had some kind of abnormality and genes in the liver also carried a 'significant' number of abnormalities.

The scientists believe that something in the nuclear transfer process used in cloning may lead to abnormal gene expression. Jaenisch said 'the nuclear transfer procedure interferes with normal programming and this leads to multiple genes being not correctly expressed'. The findings may explain why a number of cloned animals either die in utero or shortly after birth, and why many of those that do survive have various physical problems, including obesity, pneumonia and liver failure.

Jaenisch said that the research should have no effect on therapeutic cloning, as the embryonic stem cells taken from cloned embryos appear to function normally.