Autism spectrum disorder (ASD) is a neurodevelopmental disability caused by differences in the brain. Science to date doesn’t know the exact causes of these differences for most people with ASD. There are multiple causes of ASD, although most are not yet known, it’s been known to be an interplay of some genetic and environmental factors.
Source: https://www.indiatoday.in/information/story/world-autism-awareness-day-2021-check-early-signs-of-autism-and-parenting-tips-1786351-2021-04-02