Autism Spectrum, the DSM-I, and the DSM-III
Autism was not a DSM category until 1980. Under the DSM-I, children with autistic behaviors were diagnosed with schizophrenic reaction, childhood type. Adults were diagnosed with either schizophrenic reaction, paranoid type or schizoid personality disorder.
Researchers and clinicians certainly talked about autism, even under the DSM-I. However, the standard view was that it was, in children, a symptom of childhood schizophrenia.
Here is the statement in the DSM-III (1980) in which the American Psychiatric Association discusses this gradual change in thinking:
“Some believe that Infantile Autism is the earliest form of Schizophrenia, whereas others believe that they are two distinct conditions. However, there is apparently no increased incidence of Schizophrenia in the families of children with Infantile Autism, which supports the hypothesis that the two disorders are unrelated.”
http://www.psychiatryonline.com/DSMPDF/dsm-iii.pdf