High-risk bone marrow transplants partially cured five children with a potentially deadly genetic defect in which proteins that hold layers of skin together are absent, U.S. researchers said Wednesday.

But one other child died from side effects of a drug used to prepare for a transplant and a second died from a post-transplant infection.

People with recessive dystrophic epidermolysis bullosa, or RDEB, are plagued by painful blisters on the skin, mouth and throat, caused by the slightest trauma that can expose the body to infection and, in some cases, an aggressive form of cancer.

With the new treatment, "there was improved healing, fewer blisters, and their quality of life was positively affected. They could do things they couldn't do before, like ride a bicycle or go on a trampoline," said Dr. John Wagner of the University of Minnesota, who worked on the study.

It was published in the New England Journal of Medicine.

In addition, the patients' improvement progressed with time, he said. All five children who survived showed improvement within 100 days, although the pace varied widely, he said in a telephone interview.

Because of the high risks involved in bone marrow transplants, only the sickest patients with the rare condition — affecting 1 in 50,000 — have been considered candidates for a transplant, Wagner said.

Wagner reported on results of the first seven attempts, which took place at the University of Minnesota Amplatz Children's Hospital. Six other children have subsequently been treated with good results, he said.

Researchers are now trying to isolate the cells of the bone marrow best able to fix the defect and join layers of skin.

HIGH COST

The treatment, including the cost of the transplant, is between $500,000 to $1 million. But routine care for children with the collagen defect already costs about $30,000 a year and can rise due to frequent hospitalizations and complications of the disease.

"These kids have horrible pain, chronic infections of the skin, multiple hospitalizations, and systemic infections," Wagner said. They frequently can't eat or refuse to eat because of the pain. Often they die of chronic malnutrition and chronic blood loss."

Dr. Jakub Tolar, also of the University of Minnesota, said the treatment was unique because it showed that the effects of a bone marrow transplant can extend beyond the blood.

"What we have found is that stem cells contained in bone marrow can travel to sites of injured skin, leading to increased production of collagen, which is deficient in patients with RDEB," Tolar, who worked on the study, said in a statement.

Dr. Lenna Bruckner-Tuderman of University Medical Center in Freiburg, Germany, said in a commentary that the therapy represented a leap forward but expressed caution.

Because the disease can wax and wane, "it is difficult to determine how much of the clinical improvement in the children was due to transplantation and how much was due to a long period of careful medical attention, protection from trauma, and standardized wound care," Bruckner-Tuderman said.