When 10-month old Rhys Evans was successfully treated with gene therapy in April last year, he made headline news. Little Rhys had been born with a rare genetic condition, Severe Combined Immuno Deficiency (SCID), which meant he had no immune system with which to fight off infections.

Using a pioneering treatment, doctors took stems cells from his bone marrow and infected them with a retro-virus which had the correct genetic code inserted into its genes. The virus then replicates by incorporating its genetic code into the cell it has infected, so that when the cell subsequently divides it carries the viral genes instead of (in this case) the faulty genes of its original genetic make-up. These infected cells, once injected directly into Rhys, resulted in an effectively working immune system.

Although the procedure had been carried out with successful results twice before in the Necker-Enfants Malades clinic in Paris, it was a landmark for medical science in the UK.

The treatment at a specialist gene therapy laboratory, in Great Ormond Street Children's Hospital, was partly funded by the charity, Jeans for Genes.

Jeans for Genes, was set-up to raise both awareness and funds for children suffering from serious illnesses as a result of inherited genetic conditions. Once a year the charity organises a national appeal whereby people are encouraged to wear their jeans to work to raise money and show their support.

Jeans for Genes is organised by four national charities, the Great Ormond Street Hospital Children's Charity; The Primary Immunodeficiency Association; The Society for Mucopolysaccharide Diseases, and The Chronic Granulomatous Disorder Research Trust.

Jeans for Genes estimates that as many as one baby in every 33 is born with a genetic disorder or birth defect - one born every 30 minutes - although not all of these children will go on to develop a life-threatening condition.

Genetic diseases are caused by one or more missing or faulty genes. The human body is comprised of 23 pairs of chromosomes (half of which are inherited from the mother's egg and the other half from the father's sperm) which are comprised of strands of DNA which incorporate our genes.

The only existing long term treatment for the more severe disorders, says Jeans for Genes, is a bone marrow transplant (BMT). "This is a highly risky procedure," it says, "and is dependent on finding a suitable bone marrow donor and the child being well enough to undergo chemotherapy". For the majority of children with disorders which can be treated with BMT, the charity says, actually undergoing this procedure is simply not possible.

The success of gene therapy in the case of Rhys Evans, opens the door for the future possibility of treating other inherited disorders such as Mucopolysaccharidosis (MPSI) - a condition where an enzyme deficiency leads to the accumulation of complex carbohydrates in the body's cells, leading to progressive dysfunction of cellular, tissue and organ systems - and Pompe disease, where an abnormal enzyme results in glycogen building up in cells, preventing them from functioning correctly.

Indeed Dutch scientists have already made considerable headway in animal research for an Enzyme Replacement Therapy for Pompe's disease, and work is currently in progress in the USA to develop ERT for humans.

Despite such developments, however, much of the current work being undertaken in the field of gene therapy has been in cancer, and there has been a "funding gap" for corresponding research for inherited single gene disorders. Part of the problem, says the MPS Society (which campaigns for sufferers of mucopolysaccharide diseases), is that pharmaceutical companies are often unwilling to develop medicinal products for rare life-threatening conditions which affect not more than five in every 10,000 people, as they could not guarantee to recoup the cost of research and development.

It is in order to fill just such a gap - and as a result of advice from the UK Gene Therapy Advisory Committee (GTAC) - that the Department of Health has invited proposals for research on the "translational mechanisms and service developments needed to move gene therapy for the inherited single gene disorders on from a research environment to the clinic".

And although gene therapy offers hope to families of children struck down by such disorders, these kind of developments are never without their concerns, whether they be ethics or safety. As a result the DoH is also concerned to develop research programmes to monitor and assess gene therapy - whether that be the therapeutic gene itself, the delivery vehicle or the route of transmission.

These problems are especially pertinent for genetic conditions affecting more inaccessible internal organs, where it might be difficult to find a capable carrier virus to deliver the genes to the appropriate destination - or in cases where they may need to be given in a very high dose in order to be effective.

Such concerns were thrown into sharp relief when it was revealed in October last year that one of the children treated for SCID at the Necker-Enfants Malades clinic - a three-year old boy - had gone on to develop leukaemia. Although both France and the USA have suspended their trials GTAC has allowed research to continue but with "extra precautions".

The decision was welcomed by Great Ormond Street Hospital's Dr Bobby Gaspar who said that to stop the therapy trials would only result in more suffering for the child victims of genetic disorders. "Ethically," he said, "it is the right thing to do."

Jeans for Genes Day, www.jeansforgenes.com, is held on Friday October 3