The story of four-year-old Riley Mulvany, from Darlington, has highlighted the world-beating role of a North-East medical unit. Health Editor Barry Nelson reports.

NEWCASTLE General Hospital's Stem Cell Transplant Unit for Primary Immuno-deficiency is one of only two such specialist facilities in the country.

Along with the unit at Great Ormond Street Children's Hospital, in London, the Newcastle centre treats children with severe disorders of the immune system.

It has an international reputation for the latest therapy.

Doctors at the unit, which includes the Severe Combined Immuno Deficiency Disease Syndrome unit, or Scids, are probably world leaders in terms of the number of children with chronic granulomatous disorder (CGD) they have treated through bone marrow transplants.

CGD is a rare and life-threatening inherited genetic condition, which affects about four million people.

Sufferers are born with a faulty gene in their bone marrow, meaning the white blood cells cannot fight infections.

People with CGD have to take powerful antiobiotics and antifungals every day and, although the condition can be partially treated with drugs, it is life shortening unless the patient's immune system can be replaced by a bone marrow transplant from a donor.

Doctors at the Newcastle unit are increasingly using stem cells derived from the umbilical cords of babies to treat immune system disorders.

The unit, which was founded in 1993, has saved many young lives by providing advanced treatment not available anywhere else outside London.

This includes a combination of intensive drug therapy and different forms of transplants to help give children whose immune systems have failed to fight off everyday infections, that could prove fatal.

The unit on ward 23 at Newcastle General Hospital also includes the bone marrow transplant unit and an isolation ward, or "Bubble Unit", where children undergoing immunotherapy treatment are protected inside an airtight bubble from potentially dangerous germs.

Dr Terry Flood is one of the consultant paediatric immunologists who works on the unit.

"We see quite a broad range of children with serious, life-threatening diseases of the immune system. There are lots of different treatments, including the use of antibiotics and replacement antibodies, but there are some groups of children where this is not enough. Sometimes this means they need a new immune system," said Dr Flood.

In recent years, experts have realised that stem cells derived mainly from bone marrow can be used to give children with a range of immune system disorders the chance to develop a working system of their own.

Without an immune system, which relies on a healthy bone marrow to produce bacteria-fighting white blood cells, children are at risk of serious illness or death if they are exposed to common germs.

Before children are given bone marrow transplants they have to undertake aggressive chemotherapy to kill off their existing white blood cells.

During this period, they have to live inside a "bubble" of pressurised sterile air for several weeks. Any infection can be life-threatening.

After donated stem cells from bone marrow - or other sources - are transfused into the patient they have to spend months inside the "bubble" until their immune systems are strong enough to fight infections.

The Newcastle unit has treated 17 CGD patients with bone marrow transplants - thought to be a record.