As a 24-year-old with autism*, my communication style is pretty much the same both in speech and in writing. It is very formal and employs an extensive vocabulary as well as frequent adherence to the rules of grammar and technical usage. Upon hearing of my pedantic speech style, Cristi Walters, a social skills coach at Behavior Plus, Inc., commented that I could "speak lawyer" - and perhaps I could.
*Note: When I say "autism", I mean "autism spectrum disorder", or "ASD" for short - the new DSM-5 terminology for autism. When I need to specify the older definition of autism, as opposed to Asperger's syndrome or PDD-NOS, I say "classical autism".