The third paragraph:

> Now, a new study in The American Journal of Psychiatry has found that brains of autistic people have fewer of a specific kind of receptor for glutamate, the most common excitatory neurotransmitter in the brain. The reduced availability of these receptors may be associated with various characteristics linked to autism.

Reduce receptors. This might suggest a _developmental_ or genetic link. Think of this more like "height" or a particular "facial feature" of a person.