A dual diagnosis of Asperger's and Schizophrenia is not allowed in the DSM-IV, but I don't know why. Maybe its money, people with Schizophrenia are proscribed expensive drugs to treat their condition but there are not drugs for AS - so maybe psychiatrists and drug companies worry that if Schizophrenic people are diagnosed with AS as well, they will not have to take drugs anymore = less profit.
Prof. Nash may not know about Asperger's. Though interestingly, I saw him speaking on TV recently. He spoke about how he discovered that people experience emotions, and that before he did not understand that emotions affected people. He went on to say that all his old work on Game Theory was wrong - because it did not take into account people feelings. Only an autistic person can have such problems with emotions like that - and then discover them at some point. By coincidence, I talked about not understanding peoples emotions in my youtube video (I had the same problem).
The essential features of Asperger's Disorder (DSM-IV) are:
Criterion A. Severe and sustained impairment in social interaction
Criterion B. The development of restricted, repetitive patterns of
behaviour, interests, and activities
Criterion C. The disturbance must cause clinically significant impairment
in social, occupational, or other important areas of
functioning.
Criterion D. In contrast to Autistic Disorder, there are no clinically
significant delays in language (eg: single words are used
by age 2 years, communicative phrases are used by age 3
years).
Criterion E. There are no clinically significant delays in cognitive
development or in the development of age-appropriate
self-help skills, adaptive behaviour (other than in social
interaction), and curiosity about the environment in
childhood.
Criterion F. The diagnosis is not given if the criteria are met
for any other specific Pervasive Developmental Disorder or
for Schizophrenia.