Connor, a healthy baby boy, has made history. He is the first child to be born after his parents had the entire genomes of a batch of their IVF embryos screened for abnormalities, with the intention of picking the healthiest for implantation.
The technique could increase the number of successful pregnancies from IVF. And although the researchers stopped short of actually sequencing the boy's genome, the advance is proof that this could be done – potentially ushering in an era of designer babies.
IVF accounts for between 1 and 5 per cent of all births in developed countries, but it is very inefficient. An estimated 80 per cent of embryos either don't implant or miscarry, while only a third of IVF cycles result in a successful pregnancy, largely due to abnormalities in the number of chromosomes an embryo possesses.
"If you take a woman in her early 30s, around a quarter of her embryos will be abnormal. For a woman in her early 40s, it's around three-quarters," says Dagan Wells at the University of Oxford, who pioneered the new technique. The problem is that many abnormal embryos look normal under a microscope. "We need better ways of working out which embryo is the one that we should implant," says Wells.
To do this, he first took cells from seven 5-day-old embryos and extracted their DNA. He then used a technique called next-generation sequencing (NGS) to assess the number of chromosomes in each cell. This involves breaking the DNA into fragments that a computer then reads and predicts where on the chromosome each fragment came from. The sequence of an entire genome can be read in this way – although Wells's team didn't do this. They were merely interested in the proportion of DNA coming from each chromosome.
DNA library
In earlier studies, the team had compared the DNA fragments produced using NGS from healthy cells, those taken from abnormal embryos and those taken from cells with known chromosomal abnormalities. These were used as a library against which the DNA from the seven embryos could be compared.
Of the seven embryos, three were found to be normal, and one was implanted into the mother, resulting in the birth of Connor in Pennsylvania last month (see "Making a baby the scientific way"). A second woman is also expecting a baby after undergoing the same process. Neither woman has a history of inherited disease, they merely wanted to maximise their chances of having a baby through IVF.
The hope is that by selecting only healthy embryos for implantation, more women will become pregnant and fewer will experience miscarriages. Recent clinical trials of a related technique called pre-implantation genetic screening have suggested that the method could boost the implantation rate by around a third, while the miscarriage rate could be halved. The big advantage of using NGS is that multiple embryos could be screened simultaneously, significantly reducing the cost.
"This isn't going to solve the problem of reproductive ageing, as a couple in their early 40s may find they have no healthy embryos from which to choose," says Wells. However, it should boost the success rate for IVF in younger women, and also avoid the storage of embryos that have no chance of growing into a healthy baby.
The technique can also be tweaked to allow mutations in any gene of interest to be examined, such as those that cause cystic fibrosis. "This potentially gives us the opportunity to look at multiple genes and chromosomal copies," says Stuart Lavery, director of IVF Hammersmith, one of the UK's largest IVF units. "It gives us a very powerful tool for pre-implantation genetic diagnosis."
Misuse potential
However, the fact that NGS can be done on a single cell from human embryos also raises the potential for misuse. Last year, researchers in the US sequenced the entire genome of an 18-week-old fetus using fragments of fetal DNA in the mother's blood along with DNA samples from both parents. Wells's technique shows that it's possible to do this far earlier – before an embryo has even implanted in the uterus.
"It shows that there is the potential for getting an unprecedented amount of information about an embryo before it's transferred to the womb," says Wells, who presented his technique at the annual meeting of the European Society of Human Reproduction and Embryology in London today. "We need to be very careful that this isn't used for trivial, non-medical reasons."
Earlier this year, Dutch researchers published a paper suggesting that eye and hair colour can be predicted from a DNA sample (Forensic Science International, DOI: 10.1016/j.fsigen.2012.07.005), and they are now using such tests to help police identify suspects or victims of crime. The same group is also developing tests to predict the shape of facial features, such as prominent cheekbones or a large nose, and complexion.
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