Healthy twins born after new embryo test
Dr Jess Buxton
Progress Educational Trust22 November 2006
The first babies to be conceived following the use of a new embryo testing technique have been born in the UK. Twins Freddie and Thomas Greenstreet were born at Guy's Hospital, London, after their parents used a procedure called preimplantation genetic haplotyping (PGH) to identify IVF embryos free from cystic fibrosis (CF). Jim and Catherine Greenstreet, who are both healthy carriers of the inherited condition, already have two daughters - one of whom has CF.
PGH is a variation of preimplantation genetic diagnosis (PGD), which involves taking a single cell from a 2-4 day old IVF embryo, performing a genetic or chromosome test on that cell, and then returning one or two unaffected embryos to the womb. PGD is expensive, and its success rate is usually lower than that of 'standard' IVF because doctors have fewer healthy embryos to choose from. At present, PGD can only be used for disease mutations that are well characterised, and for which genetic tests are already available. It can also be used to treat families at risk of passing on 'X-linked' disorders that usually affect only boys, by selecting female embryos. However, the new technique could potentially overcome both these limitations.
In PGH, instead of detecting the mutation itself, scientists look at a set of nearby DNA 'markers' that can distinguish the chromosome with the faulty version of the gene from one carrying the healthy version. One of the advantages of PGH is that it can be offered to families carrying rare mutations - like the Greenstreets - as well as those with more common, previously identified mutations. It also means that for families affected by an X-linked disease, such as Duchenne muscular dystrophy (DMD), doctors will be able to distinguish affected male embryos from unaffected ones - potentially increasing the number of healthy embryos that can be returned to the womb.
As well as being the first PGH babies, the Greenstreet twins were also the 100th PGD birth at Guys. Mrs Greenstreet said: 'At one point we didn't think that we would be able to have any more children, so it is quite something to have two happy, healthy babies, and for them to have the extra special honour of being the Guy's and St Thomas 100th PGD babies and the UK's first PGH babies'.
Rosie Barnes, chief executive of the Cystic Fibrosis Trust, said that couples at risk of having a child with CF are often those who already have an affected child. 'Knowing that CF is a life-threatening disease and that living with the daily burden of physiotherapy, oral, nebulised and intravenous antibiotics places a huge strain on all involved, many do not wish to bring another child with CF into the world', she told BBC Online News. 'People should always be given the right to make their own informed choice, and this new development in PGD extends this choice', she added.
However, Josephine Quintavalle, of pro-life group Comment on Reproductive Ethics, said that 'it is not about the babies who have been born. It's about the babies who have not been allowed to be born. It sends a particularly bad message to children with cystic fibrosis - that society would prefer that they had not been born'.
Reproduced with permission from BioNews, an email and online sources of news, information and comment on assisted reproduction and genetics.