Capitalize "autism" when:
* It refers to the condition itself: "Autism is a neurodevelopmental disorder."
* It's part of a proper noun: "The Autism Society of America."
* It's used as an adjective: "She has an autistic son."
Don't capitalize "autism" when:
* It's used as a general descriptor: "The doctor diagnosed him with autism."
* It's part of a phrase like "people with autism": "This program supports people with autism."
General guideline: Treat "autism" like any other medical condition. Capitalize it when referring to the specific condition, and use lowercase when it's a descriptive term.