What is a Disability?

I received bad news last night that was devastating. My little grandson was born to a mother who used meth and opiates while she was pregnant with him. He has some problems and had been diagnosed with ADHD, Autism Spectrum, RAD, PTSD among a few others. It has taken 4 years to get approval for neuro testing but we finally were able to get him in to see a specialist. The results are worse than I expected. He is in the 5th percentile of severe neuro disorders. My heart is breaking.  He is such an intelligent little guy. His intelligence is 123% higher than average. WOW! But I'm not sure where we go from here...