Dr. Kirsty Horsey, Progress Educational Trust
29 June 2004
[BioNews, London]
BioNews reporting from ESHRE conference, Berlin: A form of IVF in which a single sperm is injected directly into the egg appears to slow down the growth rate of the resulting female (but not male) early embryos, according to a new Dutch study. The scientists, based at the Academic Hospital Maastricht, say their findings suggest that intracytoplasmic sperm injection (ICSI) interferes with key genes involved in embryo development. The team, lead by John Dumoulin, looked at the sex and number of cells in 330 blastocysts from conventional IVF cycles and 322 blastocysts from ICSI cycles, collected over a five year period. They found that both the male and female embryos created using IVF had similar numbers of cells (around 50). However, the female embryos created using ICSI had around 20 per cent fewer cells than the male ICSI embryos. 'Our work has clearly shown that ICSI is a significant factor in influencing growth rate, although we do not yet understand why', said Dumoulin.
The researchers also found that X-chromosome inactivation ? the process by which one of the two X-chromosomes is randomly 'switched off' in every cell of a female embryo - was disrupted in the ICSI embryos. X-inactivation works in a similar way to genomic imprinting, the switching off of certain genes during gamete development, according to whether they are maternal or paternal in origin. Previous studies have linked IVF and ICSI to a slightly increased risk of rare genetic disorders caused by a failure of genetic imprinting, for example Angelman syndrome and Beckwith-Wiedemann syndrome.
However, in both the imprinting disorder research and the latest study, it is not yet clear whether it is the IVF procedure itself causing problems, or some feature common to couples affected by subfertility. Dumoulin says the next step is to measure whether the embryo growth differences are restricted to the pre-implantation period, or whether they are present and measurable at a later stage of development. 'If these differences were to be perpetuated at a later stage it would clearly be significant for clinical practice', he said.
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Reproduced from BioNews with permission, a web- and email-based source of news, information and comment on assisted reproduction and human genetics, published by Progress Educational Trust.