The real, if a bit unfortunate answer is that most neuropsychiatric and neurodevelopmental (and indeed even neurodegenerative) disorders are like constellations.
Symptoms are like stars, and until we figure out exactly what’s going wrong in the bodies/brains of people with ASD, BPD, bipolar, OCD, vs. NT folks, we’re largely just drawing imaginary lines around them. Definitions always changing, often overlapping, mired in things like historical context and the sudden surge in ASD prevalence.
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