No more research on 'three-parent embryos' ?
Dr. Kirsty Horsey
Progress Educational Trust
16 October 2003
Researchers from Sun Yat-Sen University in Guangzhou, China have succeeded in creating a pregnancy using an embryo containing the genetic material of three different people. An egg cell taken from one woman was fertilised by in vitro fertilisation (IVF), creating a one-cell embryo, or zygote. The nucleus of the zygote was then extracted from the rest of the cell and transferred to an egg taken from another woman from which the nucleus (containing the cell's DNA) had been removed. Because a small amount of the genetic material of a cell is contained in mitochondria, which exist in the cytoplasm surrounding the nucleus, the resulting embryo contained genetic information from three sources. The research was presented at the annual conference of the American Society of Reproductive Medicine (ASRM), taking place this week in San Antonio, Texas.
The technique was used to impregnate a 30-year old Chinese woman who had been unsuccessful using conventional IVF techniques. Her eggs could be successfully fertilised using her husband's sperm, but were then unable to develop past the two-cell stage. Doctors thought that the problem might be with the cytoplasm of her eggs and, so that she could still have a child genetically related to her and her husband, used the nucleus of her egg but the cytoplasm from a fertile egg donor.
Five embryos created in this way were transferred to the woman's womb and three implanted, resulting in a triplet pregnancy. One of the fetuses was selectively terminated after a month of pregnancy, to increase the chances of survival for the other two. However, after 24 weeks of pregnancy, one of the remaining fetuses miscarried when the amniotic sac ruptured. As a result of a 'silent infection' triggered by the miscarriage, the last remaining fetus was delivered stillborn at 29 weeks gestation. The researchers say that there is no evidence to suggest that the technique itself was the problem; rather they believe that complications associated with the number of embryos transferred were the cause, or the care the woman received during her pregnancy.
The research was co-authored by Dr Jamie Grifo who, in 1998, presented similar work to the ASRM annual conference. Then, after first working on mice, he had transferred the nucleus of one woman's egg into another, younger woman's egg stripped of its genetic material, although this was never fertilised. At that time, the US Food and Drugs Administration (FDA) ruled that the technique should be regulated in humans in the same way as cloning using nuclear transfer, because both techniques involved transferring DNA from one cell to another. This meant that Grifo could not proceed with the research in the US without the FDA's approval. Dr Grifo then continued his research in China, where the technique was unregulated. However, within the last week, China has announced new laws on embryo research including restrictions on the use of nuclear transfer procedures in fertility treatments, so it is unlikely that he will be able to repeat the experiment. The research would also not be legal in the UK.
The researchers believe that the technique could be invaluable to women whose fertilised eggs are not capable of developing through pregnancy. Critics, however, have said that it too closely resembles human cloning. Sean Tipton, a spokesman for the ASRM called the technique 'cutting edge science', adding that it 'might help infertile women, particularly older women, have children'. He said that the actions of the FDA showed 'the perils of prohibiting rather than funding and regulating fertility research'. Dr Grifo said it was 'irresponsible' of people to compare the procedure with cloning. He said: 'Cloning is making a copy of a human being who already exists'. 'This is nuclear transfer, one element of cloning. It allows the couple to have their genetic baby, not a clone', he added.
© Copyright Progress Educational Trust
Reproduced with permission from BioNews, an email and online sources of news, information and comment on assisted reproduction and genetics.
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