In Britain we would say Asperger's syndrome.
Presumably you have read Mark Haddon's 'The Curious Incident of the Dog in the Night-Time' (2003), a novel dealing with the very subject upon which you are embarking, a teenage boy who has severe Asperger's syndrome. The book is currently adapted as a stage play in the West End, and has apparently been a great support to parents of children with the condition.
I would think it is essential reading to someone about to embark on a similar project.
Has anyone close to you been affected by Asperger's?