The genetic disease inherited by Rhys Evans is thankfully rare. It can only affect boys and occurs between one in 50,000 and one in 100,000 live births. Children born with X-linked severe combined immunodeficiency disease are extremely vulnerable to infection in the first two years of life, and the condition is fatal without rapid treatment as soon as they lose the immunity acquired from their mother.
It is usually treated with a bone marrow transplantation, and has a high success rate when marrow is taken from a matched sibling and a modest success rate when the mother or father has a match. Only a third of donors are a good match and although other donors can be found, results are patchy and recipients need extensive chemotherapy. Side-effects can include nausea, hair loss and sterility.
The condition used to be known as the "baby in the bubble" syndrome because of the extreme anti-infection measures that needed to be taken. Now most such children are treated in rooms sealed by air locks, although still the infant sees few people other than the medical team and close family.
Gene therapy was first practised on children at the Necker hospital in Paris, just over two years ago, and the results so far have been impressive. Specialists at Great Ormond Street hospital and the associated Institute of Child Health in London watched closely, and slightly adapted the technique.
The failure in the immune system is down to a faulty gene which means that the infant's stem cells, responsible for producing all the body's other cells, have not produced lymphocytes, specialist white cells that produce the antibodies for fighting infections.
The technique involves removing bone marrow cells from the infant's hip bone under a general anaesthetic . Scientists then purify the stem cells and others that have been removed and over a week mix them with a gene within a engineered virus that will act as the transport system. The mixture is returned to the boy's body like a blood transfusion. The corrected bone marrow then generates new immune cells which pass into the bloodstream.
Injections
The Great Ormond Street doctors say they use a slightly different virus from the French doctors, one that can cause cancer in mice but has been disabled. They believe it is more efficient at targeting the gene replacement into stem cells.
Patients still face months in hospital after the procedure and months more at home receiving injections of immunoglobulins, administered by their parents, and oral antibiotics.
Similar procedures will soon be tried in London on children suffering another genetic disorder, called chronic granulomatous diseases, where the white blood cells responsible for tackling bacteria and fungi invading the body are present but do not work.
It again is caused by the lack of a gene. Chemotherapy will still be needed for this treatment. The London team believe gene transfer to beat blood disorders such as sickle cell anaemia could follow within the next 10 years.
