It's also true that none of the symptoms of autism apply universally. I'm good friends with an autistic man, he's got a special interest for a certain branch o

It's also true that none of the symptoms of autism apply universally. I'm good friends with an autistic man, he's got a special interest for a certain branch of mathematics and swing dance. He's also great with regards to social interaction, he's seemed to keep close connections with every person he comes across when he's traveled. There's a saying that "if you've met one person with autism, you've met one person with autism", symptoms present differently in everyone and they're highly responsive to environment. As a trend I'd say special interests are probably a decent contender for a hallmark, probably along with language difficulty and eye contact avoidance.