RCW 48.01.035

The term "developmental disability" as used in this title means a disability attributable to intellectual disability, cerebral palsy, epilepsy, autism, or another neurological condition closely related to an intellectual disability or to require treatment similar to that required for persons with intellectual disabilities, which disability originates before such individual attains age eighteen, which has continued or can be expected to continue indefinitely, and which constitutes a substantial limitation to such individual.