Stephen Wiltshire is probably the greatest artist living and the fact he was born with autism and function as he does is remarkable but I'm not surprised. I have a nephew who was born with autism and he is functioning on a genius level but is the most kindest, humble person I know. Autism is when brain cells develop too close to one another and causes the synapses to misfire. If a child is lucky enough the wiring of an autistic mind can endow genius in certain skills and one can have a functional life.
My nephew is a pharmacist, married to a beautiful woman and have a son. I'm so proud of him. When he was a kid I wondered how he would fit in society, he's cool but he lacks a bit on the social side but have good friends. He has a great memory and a mind for math. He does not ever use a calculator for example and he can remember big paragraphs from books with one reading.
I have a 2nd cousin who is autistic but he is completely trapped in his mind. I never heard him utter a word. I have not seen him in years perhaps he has made some progress he is in 40's.
To be autistic and functional can be a gift but you will lack somewhere. Many people are very smart have IQ's much above 160 which is considered genius. Barak Obama IQ is 164 but keep in mind there are millions of geniuses just walking around not doing much many of them sitting in jails caught up in the mess of life. Albert Einstein flunk the 5th grade and his IQ was around 160 you can't assume too much about one's IQ because actually Emotional Intelligence determines more how you use your mind and how motivated you are, EI is more important than intelligence.
Only a very small amount of people have taken an IQ test as children or adults. People who are noted to have really high IQs bumping 180 - 200 are only the ones we know about likely many are walking around hardly doing much is smarter, we just don't know it.