A disabled dependent does not increase your standard deduction. Your dependent son should qualify for a $500 credit for "other dependent."
Checking the "disabled" box for a dependent does not result directly in extra deductions or credits. It may make you eligible to claim a person who could not otherwise qualify to be claimed as a dependent, and it may make you eligible for certain other benefits such as the dependent care credit, if you have to pay for daycare for the dependent while you and your spouse work.
