Does a diagnosis of Down Syndrome mean a person is 'disabled' for tax purposes?

[xmasbaby0]

Maybe----but how old is the person?   Are you referring to a child or an adult?  

[MaryK4]

You have a permanent and total disability if you can't engage in any substantial gainful activity because of your physical or mental condition. A qualified physician must certify that the condition has lasted or can be expected to last continuously for 12 months or more, or that the condition can be expected to result in death.

[xmasbaby0]

Do I get a credit or deduction if my child is disabled?

If your child is older than 12 and you need to pay someone to take care of him while you work, you can say he is disabled and you can still get the childcare credit on your federal return.   Or if he is 19 or older you may still be able to claim him as a qualifying child dependent on your federal return.

Aside from those things, there is no federal tax advantage to saying that your child is disabled.   Your state tax laws might be different.