An amendment won't do anything. You either owe or don't. You can try the Taxpayer Advocate service. https://www.irs.gov/taxpayer-advocate
The IRS defines handicapped in the following information. If you son fits this category and you wish to continue to fight for your rights, then you should do so. What time limit ae you referring to? Did they give you a time limit on the notice. Some notices allow you to disagree, partially agree or totally agree. You can return the notice with your response in the alotted time.
What Is Permanent and Total Disability?
A person is permanently and totally disabled if both 1 and 2 below apply.
1. He or she can't engage in any substantial gainful activity because of a physical or mental condition.
2. A qualified physician determines that the condition has lasted or can be expected to last continuously
If he does not meet this criteria, you do owe the IRS.
