This is the IRS definition of permanently and totally disabled -
IRS publication 501 - https://www.irs.gov/pub/irs-pdf/p501.pdf#page=13
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.
