IRS definition for permanently and totally disabled -
Permanently and totally disabled. Your child is permanently and totally disabled if both of the following apply.
• Your child can't engage in any substantial gainful activity because of a physical or mental condition.
• A doctor determines the condition has lasted or can be expected to last continuously for at least a year or can lead to death
If the child is under the age of 19 designating them as disabled does not give you any tax benefit, other than using the Child and Dependent Care Credit.
