Infertility specialists have expressed concern that media coverage of a technique claiming to virtually guarantee the sex of a fetus might have raised unrealistic expectations about its potential to prevent sex linked inherited conditions.
US researchers reported that the technique, which uses flow cytometry to separate sperm carrying X and Y chromosomes, was “unambiguous in assigning gender in 90 per cent of 284 embryos” in which it was used. Of these, 92% were female and 8% were male. When the group had previously carried out preimplantation genetic diagnosis, on embryos in which the sorting technique had not been used, they had found more or less equal numbers of male and female embryos. The research was presented at last week's meeting of the European Society of Human Reproduction and Embryology in Lausanne, Switzerland.
The technique is being promoted under the brand name MicroSort and was described at the meeting as being the first “sex sorter” of its type to be used for human fetal sex selection.
Harvey Stern, of the Genetics and IVF Institute, Fairfax, Virginia, reported: “We have used MicroSort in 14 preimplantation genetic diagnoses cycles for six different X linked genetic disorders, resulting in 112 embryos for biopsy.” The group also reported results from couples undergoing in vitro fertilisation “because they wanted a girl to balance their families.”
The sperm sorting technique is based on the fact that the X chromosome has greater mass than the Y chromosome because of its higher total DNA content. Sperm are sorted by DNA analysis with fluorescence in situ hybridisation (FISH) and the sperm are then separated by flow cytometric separation according to whether they bear X or Y chromosomes.
Robert Winston, professor of fertility studies at Imperial College, London, said: “This is not a completely new technique. Flow cytometry was originally developed [for sperm separation] several years ago in Cambridge.”
Most UK infertility clinics have the technique. Professor Winston was concerned about the lack of data published in peer reviewed journals by the Fairfax group, despite the fact that the group had been working on it for at least three years.
“We need to see the data before we can comment on the efficacy and safety of the technique,” he said.
He had some doubts about possible effects of the procedure on the sperm tested. “The procedure itself might change the nature of the DNA and give a long term risk of damage to the children born.”
Professor Winston was also concerned that the new technique might not be accurate enough to be used for preventing sex linked chromosomal disorders. “Preimplantation genetic diagnosis is the only reliable method based on current data,” he warned.
Professor Winston also considered that before accurate sex selection techniques become widely available, there should be careful consideration of how they should be used, particular for people simply preferring a child of one sex or the other.
DAVID AUSTIN
Figure.
This photograph is from the “Women of the World” exhibition, organised by the International Planned Parenthood Federation to mark World Population day on 9 July. The pictures show the human face of suffering that statistics often hide. The images reflect the desolation, poverty, and loneliness of women, but also their hope and friendship. The show is at the “art attack” project in Hoxton Square, London, until 15 July.