Autism is defiantly is known to run in families that combined with what you described is some definite reason for suspicion. I would just say I suspect I am Autistics or have autistic triaits. If you have not done this yet I would talk to your sister about all your concerns. She knows about living as an Autistic person and knows your parents.
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Professionally Identified and joined WP August 26, 2013
DSM 5: Autism Spectrum Disorder, DSM IV: Aspergers Moderate Severity.
“My autism is not a superpower. It also isn’t some kind of god-forsaken, endless fountain of suffering inflicted on my family. It’s just part of who I am as a person”. - Sara Luterman