In x-linked ald , which strikes mainly boys , patients develop neurological symptoms such as seizures and loss of vision around age 6 to 8 , and within months they become paralyzed , deaf , and eventually die .
But the only widely accepted way to stave off ald is a bone marrow transplant , which is risky -- 20 % to 30 % of patients die or have serious complications -- and works best if the donor marrow comes from a sibling .
The treatment , in which the virus delivered a therapeutic gene , marks the first time gene therapy has been successfully used against x-linked adrenoleukodystrophy ( ald ) -- a disorder that is always fatal if untreated .