Fifty years after Watson and Crick identified DNA, advances in gene therapy are opening up huge opportunities for the treatment of conditions like cystic fibrosis, muscular dystrophy, Huntington's, hepatitis C and some forms of cancer.
The possibilities however are multiplying faster than society can absorb and discuss the ethical implications of such work, let alone legislate limits to it. Is it right, for example, to tamper with genes that will be passed on to succeeding generations, even if there appear to be potential medical benefits from such work?
As Peter Whittaker, a research scientist and member of the Irish Council for Bioethics, set up last year by the Royal Irish Academy, points out below, such controversial "germ line" therapy may currently be legal in Ireland - but should it be?
"There are many human diseases that result from the inheritance from a parent of a single faulty gene. Fortunately these diseases are individually mostly quite rare but, for the unfortunate few, they can have serious consequences.Gene therapy - the insertion of a fully functional gene into the DNA of the appropriate body cells of the sufferer - holds out the prospect of real cures for a number of their diseases.
One disease where there are prospects of cure using gene therapy is called severe combined immunodeficiency disease (SCID).
Sufferers from the disease lack a competent immune system. These are the so-called bubble babies who must live in an environment totally isolated from physical contact with any possible source of infection.
Several trials are under way and one of these, which has been taking place in France, underlines the uncertainties associated with the early stages of this research. Although for most of the children in the trial, the gene therapy has been successful, two of the patients developed leukaemia.
The problem was that the virus that was used to carry the necessary gene to the DNA of the white blood cells inserted into a gene that kept unrestricted proliferation of the cells in check.
Cutting into this regulatory gene caused it to be inactivated thus allowing uncontrolled proliferation of the white cells, that is leukaemia.
This type of gene therapy is referred to as "somatic" gene therapy because it is targeted at the DNA of particular types of body cells. It will not affect cells which give rise to eggs or sperm and consequently the inserted gene will not be passed on to subsequent generations.
The general view is that this approach to treatment of genetic diseases is, in principle, ethically acceptable and is a logical extension of modern therapeutic medicine.
Clearly there is some way to go before problems of the kind mentioned above are ironed out, but we can be optimistic that, perhaps within the next 20 years, somatic gene therapy will become a real possibility for treating several genetic diseases.
A somewhat different type of gene therapy is referred to as germ line gene therapy (GLGT). There is the possibility that a gene may be inserted into the DNA of eggs, sperm or very early embryos in order to cure a genetic disease. In such cases, the inserted gene will show up not only in the body cells of persons that come from such eggs, sperm or embryos but also in the eggs or sperm of that person. This means that the altered DNA will be passed to the next and subsequent generations.
GLGT has generally been considered unethical. In the first place, the process of inserting a gene into egg, sperm or embryo is considered too hit-or-miss at this stage to risk the possible severe developmental defects in any child born from such a procedure. In addition, there is the important ethical question of whether it can be acceptable to cause genetic modification of as yet unborn or even unconceived individuals.
It has now been reported that up to 30 genetically altered babies have been born, 15 of these from a single research programme in the United States. These children were produced by IVF following genetic alteration of eggs from women with fertility problems.
What happened here was somewhat different from the insertion of a gene into the DNA of egg cells as described above. In fact, human cells contain two lots of DNA. The vast bulk of the DNA is located in the nucleus of the cell.
There is, in addition, a small quantity of DNA located in structures within the cytoplasm of cells, called mitochondria. These are a cell's energy machines, breaking down foodstuffs to release the energy necessary for all of the cell's activities.
The DNA in the mitochondria is quite distinct from that in the nucleus. Researchers reckoned that defects in the mitochondrial DNA of the egg cells might be the cause of the infertility. They removed cytoplasm, containing mitochondria, from developing egg cells from fertile donors and injected it into egg cells from women with fertility problems. These eggs, now with two types of mitochondrial DNA, were fertilised in vitro and implanted into the mothers' wombs. In some of the cases, apparently healthy babies were born.
One year later, genetic fingerprinting tests on two of the babies showed that they had maintained both the mothers' and the donors' mitochondrial DNAs.
These procedures were clearly a type of GLGT as the donor genes will almost certainly show up in the mitochondria of eggs of any adult women arising from these babies. Any type of GLGT is expressly illegal in some countries. In Ireland, mitochondrial GLGT would probably be legal at present.
These experiments seem to have been successful although the scale of the success is not yet clear.
But should this research ever have been carried out? What were the potential risks? Did the results of the programme justify any risks that were taken? It is probably too early to give full answers to all of these questions.
There obviously were risks for the offspring and for the parents that might have had to cope with any developmental problems that might have arisen.
The risks were probably not as great as those involved in inserting genes into the DNA of the nucleus - at present still something of a lottery.
The mitochondrial genes transferred would be small in number and organised as a single block. It is probable that these would remain in the mitochondria and would be unlikely to insert into nuclear DNA.
Nevertheless there could be unpredictable problems arising from interactions between the two types of mitochondrial DNA or from the microsurgical techniques needed to inject the donor cytoplasm. Although the children appear to be healthy at present, can we be sure that problems might not arise at a later stage resulting from carrying two types of mitochondrial DNA?
The question of whether it is acceptable to modify the genetic component of future generations is a more difficult one. If it could be established that the only future effect of this type of gene therapy would be to improve the fertility of future females, it could be argued that this was commendable. However, if the acceptance of this type of GLGT would open the door even slightly to other types of GLGT, then it should not be encouraged.
We can only guess where this door may lead. I believe that one thing is clear: it would be a step towards taking decisions about what genes should or should not be passed on to our children and to our children's children.
We should think very carefully before passing through this doorway."