IT MIGHT one day be possible to genetically test individual sperm cells before using them to fertilise an egg, claims Dmitri Dozortsev of the Roger Abdelmassih Clinic and Research Centre in S茫o Paulo, Brazil.
At the moment, genetic testing during IVF usually involves taking one or two cells from an early embryo (New 杏吧原创, 25 October, p 12). If tests on these cells reveal a dangerous mutation, the embryo they came from is discarded.
A technique for screening sperm before fertilisation, together with existing methods for screening eggs, would help cut the number of embryos that have to be discarded, and might be acceptable to those who oppose the destruction of fertilised embryos on religious grounds.
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To test the idea, Dozortsev鈥檚 team exposed the DNA inside individual human sperm by digesting their coat, and then used the PCR method to make multiple copies of part of their DNA. These copies could be used for genetic tests. To see whether the sperm chromosomes survived this treatment, each sperm was then injected into an egg, which was activated by injecting cell fluid from other sperm.
The eggs 鈥渇ertilised鈥� this way underwent the very first stages of development, but many of the chromosomes were damaged and none of the embryos survived longer than three days (Reproductive BioMedicine Online, vol 7, no 4).
Dozortsev鈥檚 team say the results show that pre-conception sperm analysis might be feasible if the PCR technique could be modified to avoid damaging sperm DNA. But other experts are more sceptical, and no doctor would consider using such a method during IVF unless it was safe and reliable.
It is already possible to screen eggs before they are fertilised, by extracting what is called the polar body, which contains a set of chromosomes identical to those in the egg鈥檚 nucleus.