If it isn't present from an early age, it isn't autism. If it goes away with "cures", it, by definition, not autism. Autism is a neurodevelopmental disorder, meaning that it first becomes apparent in early childhood, and our brains are literally wired differently in a way that has been observed and proven. Our brains have more neurons activated, so that even at rest we are processing 42% more information than a non-autistic person's brain. This can explain why we often have sensory processing disorder, too.
Multiple studies have well established a genetic connection, it should not be up for serious debate.
Autism is by and large, behavioral. It can appear to get better, mainly because as we grow, we learn that others do not like our differences, so we hide them and find ways to seem more "normal". (Usually at great cost to our wellbeing, I might add.)