From neurodevelopment to psychiatric, medical practitioners have referred autism to many kinds of disorders. Apparently there are no medical tests to diagnose the disorder and behavior in general has to be observed to call someone autistic.
It is indeed a complex disorder. Centered in the brain, autism affects a child’s development in the core areas of communication, social interactions, and behavior. This is perhaps best captured by the term neurodevelopmental disorder.
In terms of diagnosis, The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR), published by the American Psychiatric Association, provides some help. The DSM-IV-TR provides a common language and standard criteria for the classification of mental disorders. Tools used to help a provider (both medical doctors and psychologists) make a diagnosis are typically clinical (e.g., patient observation and interview) and psychological (e.g., standardized psychological tests) in nature.
But a child’s physical health is also affected in this disorder. Conditions like seizures, gastrointestinal distress, eating irregularities, sensory challenges, and sleep disturbance can all be attributed to neurobiological irregularity.
So you could say it is multi-faceted: a disorder which poses many questions, many of them still unanswered, but significant research is being done to demystify the causes, diagnostic issues, and treatment endeavors.