TWENTY children have been born after doctors performed a kind of transplant surgery on the eggs of their mothers, for whom normal IVF had failed. But other experts are concerned about the long-term safety of the technique. The technique, developed by Chii-Ruey Tzeng's team at Taipei Medical University in Taiwan, involves adding more of the power-generating components of cells, called mitochondria, to eggs. The team extract mitochondria from the granulosa cells that surround eggs and inject around 3000 into each egg. This addition has a dramatic effect. In a group of women for whom IVF and ICSI had failed, it boosted the pregnancy rate per cycle from 6 to 35 per cent, Tzeng told a meeting of the American Society for Reproductive Medicine in Philadelphia this week. Mitochondria are unusual because they contain their own DNA, and Tzeng thinks the method works by replacing those with damaged DNA. In eggs, mitochondria have only one copy of this DNA, making them vulnerable to damage as women age.
In contrast, mitochondria in the granulosa cells have around five copies. Because the method involves adding a woman's own mitochondria to her eggs, it is likely to be less controversial than using mitochondria from other women, where children would inherit about 40 of the 25,000 human genes from the donor. In 2001, the Food and Drug Administration intervened to stop Jacques Cohen's team at the Institute for Reproductive Medicine and Science in Saint Barnabas, New Jersey, injecting cytoplasm, which includes mitochondria, from one woman's egg into another's. At least 30 children were born this way. And a woman in China became pregnant with triplets after the nuclei of her eggs were transferred into donor eggs before fertilisation, meaning all the children's mitochondria would have come from the donor, had they survived (New Scientist, 18 October 2003, p 12).
Last week, Doug Turnbull and Mary Herbert at the University of Newcastle upon Tyne in the UK applied for permission to use nuclear transfer to prevent children inheriting diseases caused by mitochondrial mutations in their mothers. Pressure groups attacked the idea as an unacceptable step towards genetic engineering of humans. Cohen says Tzeng's work is impressive, but he has concerns. He points out that we do not understand the consequences of moving mitochondria from one cell type to another. For instance, in eggs and early embryos mitochondria do not replicate, while they do in granulosa cells. More seriously, he says the group should have done more extensive experiments on animals to evaluate the long-term health effects. "I think that work needs to happen," Cohen says. "Then they would have much better ground to stand on."
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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