Batten disease is caused by a defective gene that fails to create an enzyme needed in the brain to help dispose of brain cellular waste. The waste piles up and kills healthy cells until the patient dies. Most victims die before they reach their teens.
The kids being experimented on WILL DIE within years without the experiment. They'll probably die anyway, but maybe more slowly. The injected neurons take over the kid's brain and make it work right.
Next step, increased usage of the death penalty with compulsory organ donation!