FDA OKs Drug That Aids ‘Bubble Babies’ : Health: The medication replaces an enzyme needed to prevent dysfunction of the immune system. It may lead to treatment of other genetic disorders.

The Food and Drug Administration on Friday approved a new drug for so-called “Bubble Boy Disease” that will enable many children suffering from the rare genetic disorder to escape their sterile plastic environments and live relatively normal lives.

Researchers said that the drug may be the forerunner of others useful for treatment of other incurable genetic disorders.

“For the first time, there is a treatment for directly correcting an inherited enzyme deficiency disease,” said Dr. Michael Hershfield, a Duke University scientist who coordinated clinical trials of the drug.

The drug, PEG-ADA, manufactured by Enzon Inc. of South Plainfield, N. J., replaces an enzyme called adenosine deaminase that is absent from children who have the disease. The deficiency results in a partial or total dysfunction of the immune system, leaving the children unable to fight common infections.

About 40 children worldwide each year are born with this form of Severe Combined Immunodeficiency Disease, or SCID. There are other causes of SCID, which annually afflicts about 100 children globally.

“If this drug is successful in replacing the missing enzyme, it represents a remarkable advance in immune system engineering,” Dr. Michael Gottlieb, a Los Angeles immunologist, said.

Some children can be cured by bone marrow transplants. But compatible marrow donors can be found for less than 20% of SCID children, and the risk of rejection is high. An alternative treatment, involving transfusions of irradiated red blood cells, provides only a fraction of the enzyme necessary.

If left untreated, most children die before the age of 2.

The condition has become known as the “Bubble Boy Disease” because some children have survived only by living for years in sterile plastic bubbles.

The most famous case was that of a Texas boy named David, who lived 12 years in such a bubble. He died on Feb. 22, 1984, from an infection, four months after receiving a bone marrow transplant from his older sister.

Another approach to treating the disease is being studied by researchers at the National Institutes of Health, who are seeking to replace the defective gene that causes the deficiency.

The drug, which will be marketed under the trade name Adagen, is the result of a new technology that attaches strands of a polymer to the enzyme to increase its circulating life in the bloodstream. The enzyme can then continuously prevent the accumulation of toxic substances and help restore the body’s ability to produce cells of the immune system, according to the company.

The treatment does not prompt the body to manufacture its own enzymes. Thus, patients must receive weekly injections of the drug for the rest of their lives.

To date, 12 children have been treated with the drug, nine in the United States and three in Europe. Since the treatment began, the company said, the children have gained weight, grown taller and “fought off infections in a manner similar to that of normal children.”

One child who underwent therapy with the drug was exposed to chicken pox but fully recovered. Before the therapy, “this infection could have been fatal,” the company said.

The first patient to get the drug was a 6-year-old Kentucky girl, who received it for more than three years through the Duke University Medical Center in Durham, N.C. Before drug therapy, she had undergone two unsuccessful bone marrow transplants, had recurrent episodes of pneumonia, was kept on oxygen therapy because of chronic lung disease and was below average in weight and height, the company said.

As a result of drug treatment, “she has been free of infection for extended periods of time in the past two years, and has steadily gained weight,” the company said. “She has also been able to attend school for the first time.”