CHICAGO - A drug used to suppress the immune system in cancer and rheumatoid arthritis has helped extend the life of a Minnesota boy struggling with a rare and deadly form of the genetic disorder Pompe disease.

A team of researchers led by Dr. Nancy Mendelsohn of Children's Hospitals and Clinics of Minnesota used a novel treatment plan using Rituxan, or rituximab, a drug used for non-Hodgkin's lymphoma and rheumatoid arthritis made by Genentech Inc and Biogen Idec.

Rituxan is a monoclonal antibody, a genetically engineered immune system molecule. The team used Rituxan in combination with the rheumatoid arthritis drug methotrexate and intravenous gamma globulin, in a bid to damp down the child's immune response.

"It seems to have worked," said Mendelsohn, who chronicled the child's case in the New England Journal of Medicine on Wednesday.

Pompe is an enzyme disease, and many of its youngest victims lack a gene that makes alpha-glucosidase or GAA, which is needed to break down glycogen, a stored form of sugar.

The resulting build up of glycogen damages the muscles, especially the heart and skeletal muscles.

Older Pompe patients often respond to enzyme replacement therapy, but many infants with the "CRIM negative" form of the disease quickly make antibodies to the enzyme and rarely see their first birthday.

Not so for Ira Brown of Minneapolis, whose symptoms first appeared at around five weeks of age.

Stymied by the poor prognosis of infants who develop the genetic disorder, Mendelsohn and colleagues decided to try suppress the child's immune system to allow him to respond to the enzyme replacement treatment.

At 2-1/2, Brown is now the oldest survivor of the CRIM negative form of the disease.

Mendelsohn is hopeful the treatment will induce tolerance to enzyme-replacement therapy, so the Rituxan may one day be discontinued.

She said the treatment approach is being tried on other children and thinks it may work for other diseases, including hemophilia A and B, Gaucher's disease and Fabry's disease.

(Editing by Cynthia Osterman)

© Thomson Reuters 2009