How did Leo Kanner distinguish early infantile autism from childhood schizophrenia?

Since the 2000s, the prevalence of autism spectrum disorder (ASD) has increased, and the diagnosis of ASD has become heterogeneous. Recently, some researchers have begun to regard ASD as a form of neurodiversity rather than a medical disorder. In this article, we re-examine the establishment process of early infantile autism, as reported by Leo Kanner, and place the current debate in a historical context. An essential issue for Kanner was differentiating early infantile autism from childhood schizophrenia, but what made this difficult was the changing concept of schizophrenia over time. We consider how this affected Kanner's arguments and how it relates to the current autism debate.