In the French trial, the virus was used to deliver a therapeutic gene to two 7-year-old boys with ALD who couldn't be matched with a bone marrow donor, which is a widely used form of treatment.
According to the National Institutes of Health, ALD is one of a group of genetic disorders called the leukodystrophies that cause damage to the myelin sheath, an insulating membrane that surrounds nerve cells in the brain.
French researchers removed blood cells from each boy and treated the cells with a modified HIV virus carrying the gene for the enzyme they lacked. The virus delivered the gene to the DNA of the blood cells.
The boys underwent chemotherapy for their bone marrow in order to allow the treated cells room to multiply. Eventually, the cells migrated to the brain as researchers had hoped.
After more than a year, the boys' blood cells were still making ALD, and their disease had stabilized or improved.
The type of ALD in question is caused by a defect in an X chromosome gene that produces a protein called ALD. It is called X-ALD and is the most common form. The childhood form is the most severe. Cells need this protein to break down certain fats so without it, the fats build up and damage the myelin sheathing.
According to the NIH, the most common symptoms associated with X-ALD are usually behavioral changes such as aggression, poor memory and poor school performance. Other symptoms include learning disabilities, seizures, difficulty swallowing, deafness and progressive dementia.