Italian researchers have used a defanged version of HIV to replace faulty genes and eliminate devastating symptoms in children suffering two rare and fatal genetic diseases.

Improved gene therapy techniques prevented the onset of metachromatic leukodystrophy in three young children and halted the progression of Wiskott-Aldrich syndrome in three others.

The advance represents a major stride for a field that has struggled to translate experimental successes in lab animals into safe and effective treatments for people, experts said. Researchers may be able to use the team's method as a template, modifying it to treat a variety of diseases.

This is "ammunition for the gene therapy world," said Dr. Theodore Friedmann, a pediatric gene therapist at UC San Diego, who was not part of the study. "The field is slowly but surely making impressive advances against quite untreatable diseases."

The scientists published results from the two clinical trials Thursday in the journal Science.

Metachromatic leukodystrophy affects just 1 in 40,000 to 1 in 160,000 people worldwide; Wiskott-Aldrich syndrome, only 1 to 10 per million males. But both illnesses are devastating. Children with late infantile metachromatic leukodystrophy, the most common form of that disease, begin having trouble walking about a year old and soon after experience muscle deterioration, developmental delays, paralysis and dementia. Most die within a few years of onset.

Kids with Wiskott-Aldrich syndrome suffer from eczema, bruising, nosebleeds and recurrent infections. Most develop at least one autoimmune disorder. A third get cancers, such as lymphoma and leukemia. Life expectancy ranges from 15 to 20 years.

The disorders are challenging when not impossible to treat. No therapy exists for metachromatic leukodystrophy. A bone marrow transplant can stop disease progression for the few Wiskott-Aldrich patients with an immunologically matched sibling, but they may experience severe side effects or death if the donor is not as close a match.

Both diseases are caused by inherited genetic mutations that disrupt the body's ability to produce crucial enzymes. In each trial, researchers took the normal form of the faulty gene and attached it to a virus derived from HIV that had been modified so that it could no longer cause AIDS.

The researchers removed bone marrow stem cells from the patients and then used the lentivirus to infect those cells with the normal genes.

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Gene therapy using HIV helps children with fatal diseases, study says

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