Wednesday, June 18, 2008

Can we create life? by Vivienne Parry

Our knowledge of, and ability to, alter DNA remains rudimentary, in spite of notable scientific advances and the persistent dream of genetic perfection. Vivienne Parry explains

Six week old human embryo

A six-week-old human embryo. Photograph: Getty

Will the parents of the future be able to use IVF and genetic technologies to dictate exactly what they want in a baby? To have a blue-eyed blond? Or one with musical ability? Super-smart perhaps? The short answer is likely to be no. So-called designer babies are not possible now and it's highly likely that they won't be possible in the future either. Here's why.

Let's say you are a pushy mum and dad who want a boy who will be a super athlete. There are some specific genes that are known to be associated with athletic ability. For instance, there's one called ACTN3. One version of it makes a protein found only in the fast muscle fibres that help sprinters produce explosive bursts of speed. One study of elite sprinters found that 95% of them had this gene variant. The problem for our pushy parents is that this gene is only one of many hundreds likely to contribute to sports fitness and performance, most of which are still unknown. So even if an embryo were to be selected that had this go-faster gene, this would not assure sports ability, let alone Olympic gold. And in any case, sports performance is about much more than just genes. It's how hard you practise, whether you have access to training and equipment, whether you are motivated, what you eat and so on.

There's another problem for our parents. If it's theirs, the embryo will have an assortment of the genes that the parents have; and if neither of them carry the right variant of ACTN3, their embryo won't have it either. Even if one of them did carry ACTN3, not every embryo they produced would have it. So they might have to screen many embryos before they found one that had it and was male.

And there's one further hurdle. The embryo would then have to be implanted in the woman's womb. Even in the best clinics, IVF only has a 40% chance of success, and if a woman is older it is much less.

At the moment, it is possible for parents who carry a genetic disease to reduce the chance that a child will be born with it in two ways. The first involves choosing the type of sperm that is used to fertilise the woman's egg. Only using sperm that carry an X chromosome to fertilise the egg means only unaffected girls are conceived.

The second technique involves screening embryos for a particular genetic disease or chromosome disorder so that only embryos free from it are replaced. This technique is called pre-implantation genetic diagnosis (PGD). It is limited to those parents whose babies are already known to be at risk and it is used to screen embryos for very specific problems, like cystic fibrosis. In Britain there have only been 500 cases of PGD, all for serious disease, since 1990, yet there are around 25,000 cycles of IVF each year.

It is currently illegal, but could you alter an embryo's genes so that a disease didn't occur? If this is done in egg or sperm cells (what's called germ line therapy), the changed gene is transmitted to future generations.

Gene silencing

Silencing a gene is a well established technique in mice, where it is used to create so-called "'knockout"' mice to study the effects of genes. Artificial DNA is introduced into mouse embryonic stem cells to silence one particular gene. The altered cells are then introduced into early mouse embryos, which are then implanted in a mouse womb. The resulting pups have some tissues with altered genes, but repeated breeding ensures mice that have all their tissues of the new type.

But very few genes have single effects and altering one can have deadly consequences. About 15% of mouse gene knockouts are lethal; others produce unexpected handicaps. In humans there is a gene that appears to be correlated with a 10-point boost in IQ. But it is also associated with a 10% chance of developing a muscle condition that can confine the sufferer to a wheelchair with uncontrollable muscle spasms. Altering genes isn't like editing a document in Word. DNA is an invisibly thin molecule coiled upon itself with the millions of letters that we can't see - trying to alter just three letters without damaging anything else is a truly daunting task. These dangers mean that designer babies are not possible now and may never be.

Building a new organism from scratch is possible. In January this year a US team reported in Science magazine how it built the entire DNA code of a common bacterium in the laboratory using blocks of genetic material. The team synthesised small blocks of DNA before knitting them together into bigger "cassettes" of genes. Large chunks of genes were joined together to make the circular genome of a synthetic version of a mycoplasma bacterium.

This technique is called synthetic biology and it combines science and engineering to build new biological functions and systems. The US group J Craig Venter Institute hopes eventually to use engineered genomes to make bacteria that can do useful things, such as produce clean fuels or take carbon dioxide out of the atmosphere.

But many people are extremely concerned by the possibilities of bio-error (or bio-terror) that artificial life creates. They say artificial microbes could have dangerous consequences if they escape into the environment or if they are used to manufacture bioweapons. At present there are no international laws or oversight mechanisms to assess the safety of synthetic organisms. Organisations such as the Royal Society are currently seeking the public's view on this technology.

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