I am very bothered by the strong possibility that a there exists a large group of autistic adults who are either undiagnosed or misdiagnosed. Demonstrations of this come up over and over in the research literature. Such is the case with Missed diagnosis of autism in an Australian Indigenous psychiatric population, which came out on Pubmed today.
This recent example is from a very specific group: Indigenous Australians hospitalized with schizophrenia diagnoses. This particular group was 215 patients. Of this group, 14 were selected (I haven’t read the paper so I don’t know how this subgroup was selected). Out of that particular subgroup, 13 were “considered” to have a diagnosis of autism.
Missed diagnosis of autism in an Australian Indigenous psychiatric population.
Roy M, Balaratnasingam S.
South Birmingham Primary Care Trust, Birmingham, UK.
AbstractObjective: The aim of this paper is to review the diagnosis among adult Indigenous patients from the Kimberley region of Western Australia who had an existing diagnosis of schizophrenia. A visit from a psychiatrist specializing in intellectual disability provided the opportunity for conducting psychiatric assessments from a developmental perspective. Method: Selected patients with schizophrenia were assessed from an intellectual disability perspective from an active case load of 215 patients. Result: Thirteen out of 14 selected patients were considered to have a diagnosis of autism when a developmental history was undertaken. Case studies are presented to illustrate the overlap in symptoms and potential for the diagnosis of autism to be missed. Conclusions: Autism spectrum disorders may be missed in Indigenous population groups. This has implications for treatment and service provision. Clinicians need to be mindful of the diagnostic possibility that an autism spectrum disorder might be masquerading as schizophrenia in the context of intellectual disability and atypical presentation.
Misdiagnosis of autistics happens. It happens in the U.S., the U.K. and elsewhere. Again, this really bothers me. It bothers me that there seems to be little focus on this issue by autism advocacy organizations, even by the research funding agencies.
Left Brain Right Brain 
Note, that this appears to be overseas doctors working in Australia. Sadly, it is quite possible that under-diagnosis of ASD applies to much of the adult Australian population since some Government funded mental health services in Australia do not regard autism/ASD as mental illness (I remain puzzled as to which part of a person they think ASD affects).