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What diseases can be treated with pre-implantation genetic diagnosis (PGD)?
In theory, PGD could be used to look for any disease caused by a single gene, as long as a test has been developed for that gene. Until recently it was only offered in the UK for diseases also checked for during prenatal diagnosis (tests done when the woman is already pregnant) – things like cystic fibrosis or myotonic dystrophy.
But in November 2004 University College Hospital was given permission to use PGD to look for a gene which causes bowel cancer. Unlike other diseases PGD has been used to screen for, bowel cancer is a late onset disease – it doesn't affect people until they are adults. The PGD centre at University College London is also investigating the possibility of using PGD for certain types of breast cancer, which are caused by a single gene.
Could PGD be used to choose the sex of a baby?
PGD can be used to look at the sex of an embryo. In fact the first PGD treatment in the UK was used to treat a sex-linked disease, Duchenne muscular dystrophy. Only male babies can inherit this disease, so PGD was used to select female embryos which will not have the disease.
In the UK it is only legal to use PGD techniques for sex-selection to prevent a serious sex-linked disease. But some other countries also allow the technique to be used for 'family balancing' – parents who already have one or more children of a particular sex can use PGD to choose an embryo of the opposite sex.
Why did Philippa Handyside's genes cause her to have miscarriages?
Philippa has a chromosome disorder. Human genes are grouped together into 23 pairs of chromosomes. Two small sections of Philippa's chromosomes have swapped places. This means some of her genes are in different places than normal – but she still has all the genes she needs.
However when an egg forms it only contains half of the mother's chromosomes. Because Philippa's chromosomes have been mixed up, many of her eggs contained too many or too few genes, so they wouldn't grow properly.
Although Philippa's problem is one that is passed down the family line, a major cause of infertility might be random mix-ups in the chromosomes when eggs form. Some scientists are developing ways to use PGD to screen all IVF embryos for chromosome mix-ups, in the hopes of improving the success rate of IVF treatments.
Could PGD be used to choose an embryo with certain characteristics, such as blue eyes, brown hair, or good musical ability?
Many characteristics are affected by more than one gene and some – such as height, musical ability, and intelligence – are also affected by the environment. Currently it is very difficult to test for more than one gene and impossible to test for multiple genes at once, so PGD could not be used to select these characteristics. Also, if the parents don't carry the genes associated with musical ability or intelligence, these genes will not be present in any of their embryos, and it would be impossible to select for them.
But even if PGD developed in such a way that it was possible to select embryos for these types of characteristics, it would be illegal to do so in most countries, as sex selection for social reasons is already illegal in most of Europe.
What diseases have been treated using gene therapy?
Gene therapy was originally developed to be used on genetic diseases where a single gene is not doing its job. A healthy version of this gene is inserted into the DNA of a patient, and the new gene does the work of the damaged one. But there is currently no way of removing the damaged gene.
Gene therapy has had the most success on children with severe combined immunodeficiency (SCID). Their immune systems do not work properly because of a faulty gene, so they must be kept isolated. Inserting a healthy immune system gene makes their immune system work far better.
Gene therapy researchers are now looking at more genetically complicated diseases, such as cancer and arthritis. In the case of cancer, the idea is that genes could be introduced that trigger the selective death of cancer cells, or that genes are used that provoke the body's own immune system into recognising and destroying cancer cells.
What are the problems with gene therapy?
Doctors use a virus to carry the healthy genes into a patient's cells. They inactivate the virus so that it does not cause a serious infection. But in one study the virus was not as safe as researchers had thought. The result was the death of an 18-year-old patient - his organs failed as a result of an immune reaction to the virus. Many studies however have used viruses to carry new genes into cells perfectly safely.
The other potential problem with gene therapy is that scientists have no control over which section of the DNA the new gene will insert into. This has led to two cases of leukaemia as a result of gene therapy treatment for SCID. The new gene inserted into the children's DNA at a point where it caused the cells to become cancerous, and the children developed leukaemia. But there have also been many cases where the gene has inserted into DNA without any harmful effect.
Because of these problems, scientists are investigating ways of getting genes into cells without relying on a virus. These include the use of microscopic fatty spheres (liposomes), the direct injection of 'naked' DNA into the body, and an artificial human chromosome.
Was Dolly the first cloned animal?
No. Clones occur naturally in animals and in humans – they are called identical twins. Identical twins have exactly the same DNA, as they grow from a single embryo that divides into two in the womb.
In the 1950s frogs became the first animals to be cloned using the cloning technique called cell nuclear transfer. Scientists took a frog egg, removed its DNA and inserted genetic material from the cell of a tadpole. Other clones were produced in the 1980s and early 1990s using the genetic material from embryos.
Dolly was special because she was the first mammal to be cloned from the DNA of an adult sheep. Since Dolly, scientists have cloned a range of mammals, including cows, pigs, mice, cats and even a mule.
Why did the scientists at the Roslin Institute want to create sheep clones, and insert human genes into sheep?
Using cloning technology, scientists hoped to produce genetically identical livestock from the best farm animals. But with cloning they could also add new genes into animals more easily.
At the Roslin Institute the scientists who created Dolly later created sheep which carried a human gene. The gene meant the sheep produced a human protein in large quantities in their milk. The protein affects blood clotting, and could be used to treat diseases of the blood in humans. Scientists thought they might be able to use genetically modified cloned sheep to produce a range of human proteins which could be used in the treatment of disease.
Where do the human eggs come from for Newcastle University's therapeutic cloning research?
Researchers at the university are trying to grow human embryonic stem cells from human eggs using cloning technology. They are doing this work alongside the IVF unit at the Newcastle Fertility Centre.
In IVF eggs from the mother are fertilised by the father's sperm in the lab. There are often a small number of eggs that do not fertilise, so they cannot grow into embryos that can be used in IVF. Patients are given the chance to donate these unfertilised eggs to the embryonic stem cell research.
Because the research relies on these donated eggs, it will take some time to see if this technique to produce stem cells will work with human eggs. The IVF clinic expects there will be tens of donated eggs available each week. Similar work at Seoul National University in South Korea needed 247 unfertilised eggs, donated by 16 women, to grow one human embryo stem cell line.
Who decides how genetic technologies like PGD, gene therapy, and cloning are used?
In the UK there are various bodies responsible for regulating genetic research. The Human Fertilisation and Embryology Authority licenses and monitors any research work involving human eggs and embryos. This includes research into human embryonic stem cells, and the therapeutic cloning work being done at Newcastle. They also regulate and inspect all UK clinics providing IVF, donor insemination or the storage of eggs, sperm or embryos.
The Gene Therapy Advisory Committee (GTAC) is responsible for advising the UK government on gene therapy research and its implications. All gene therapy trials are required by GTAC to meet accepted ethical criteria for research on human subjects. Gene therapy trials are currently limited to life-threatening diseases, where no other alternative treatments are available.
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