There remain differences, for example Rett disorder was included in ASD in the DSM-5 but in the ICD-11 it was excluded and placed in the chapter for Developmental Anomalies. Both the ICD and the DSM have been under revision and there has been collaborative work towards a convergence of the two since 1980 (when DSM-3 was published and ICD-9 was current), including more rigorous biological assessment - in place of historical experience - and a simplification of the system of classification. DSM
The American Psychiatric Associations Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR), released in 2022, is the current version of the DSM. The fifth edition, DSM-5, released in May 2013, was the first to define ASD as a single diagnosis, which is continued in DSM-5-TR. ASD encompasses previous diagnoses which included Asperger disorder, childhood disintegrative disorder, PDD-NOS, and the range of diagnoses which included the word autism. Rather than distinguishing between these diagnoses, the DSM-5 and DSM-5-TR adopt a dimensional approach to diagnosing disorders that fall underneath the autistic spectrum umbrella in one diagnostic category. Within this category, the DSM-5 and the DSM includes a framework that differentiates each individual by dimensions of symptom severity, as well as by associated features (i.e., the presence of other disorders or factors which likely contribute to the symptoms, other neurodevelopmental or mental disorders, intellectual disability, or language impairment).
In infancy, children at high risk for autism that were later diagnosed with autism were observed to have abnormally high long-range connectivity which then decreased through childhood to eventual long-range under-connectivity by adulthood. Abnormal preferential processing of information by the left hemisphere of the brain vs. preferential processing of information by right hemisphere in neurotypical individuals. The left hemisphere is associated with processing information related to details whereas the right hemisphere is associated with processing information in a more global and integrated sense that is essential for pattern recognition. For example, visual information like face recognition is normally processed by the right hemisphere which tends to integrate all information from an incoming sensory signal, whereas an ASD brain preferentially processes visual information in the left hemisphere where information tends to be processed for local details of the face rather than the overall configuration of the face. This left lateralization negatively impacts both facial recognition and spatial skills. Increased functional connectivity within the left hemisphere which directly correlates with severity of autism. This observation also supports preferential processing of details of individual components of sensory information over global processing of sensory information in an ASD brain. Prominent abnormal connectivity in the frontal and occipital regions. In autistic individuals low connectivity in the frontal cortex was observed from infancy through adulthood. This is in contrast to long-range connectivity which is high in infancy and low in adulthood in ASD. Abnormal neural organization is also observed in the Brocas area which is important for speech production.