A simple bout of chicken pox could have had an eight-year old boy knocking on death's door last year. When the disease hit this year a new drug had him back at school within a couple of weeks.

He lives in Melbourne, is one of up to 50 people in Australia who have severe chronic neutropenia (SCN), which leaves them highly vulnerable to infection.

Chicken pox poses a particular threat to these people because SCN causes persistent sores which promote the spread of chicken pox and increase the risk of blood poisoning.

People with SCN cannot produce enough white blood cells, called neutrophils,, to fight infection and, before antibiotics were developed, they usually died in their first or second year of life.

Even with antibiotics, they still suffer life-threatening bacterial infections and painful ulcers of the mouth, throat, and anal regions. They may spend months or even years in hospital on intravenous antibiotics.

Christopher and his two-and-a-half-year-old sister Hannah, who also has SCN, now have daily injections of Neupogen, which stimulates the production of white blood cells.

The treatment's success was demonstrated when this patient and his sister recovered from chicken pox about as quickly as their other sister and brother who are not affected by SCN. "If they had the chicken pox without Neupogen they would have been very, very sick indeed," their mother said in an interview.

"They would have been at death's door if we hadn't had Neupogen. We were very grateful for it, it's wonderful stuff," she said. The risk of having a life-threatening infection would have been much higher without the Neupogen," said a children's blood cancer specialist in Melbourne. "For this condition, it's doing a marvelous job."

The two children with SCN have another medical problem which prevents their bodies from storing food energy, forcing them to eat frequently and have feeding tubes inserted at night to keep their blood-sugar levels up and prevent them from falling into comas.

Their mother learned to cope with inserting the tubes into her children's throats but she could not face the daily injections of Neupogen so her husband does those.

But the injections are worth it. Her son had an ulcer the size of a ten-cent piece between his buttocks for more than 18 months before the family found out about Neupogen.

It cleared within six weeks, relieving the agony the ulcer produced every time he had to defecate.

European trials of the drug, which Australia has just approved for treating SCN, shoed it had a 90 per cent success rate, a German expert said during a recent visit to Sydney.

"Trials involving 51 people with SCN had been extraordinarily successful," noted the pediatrician of the medical school of Hannover in Germany said in an interview.

"About one in a million people are born with SCN although the genetic defect occurs more frequently in cultures where cousins marry."

Just two children out of 51 failed to respond to Neupogen in the trials that were conducted. One was treated with a bone marrow transplant and the other one died. The pediatricians patients have been taking Neupogen for up to five and a half years, suffering few side effects, although some have had bone pain.

"The drug reduced sufferer's need for antibiotics, cut stays in hospital and dramatically improved their quality of life."