Biological Implications of the Overlapping Phenomenon Between Childhood Schizophrenia and Autism Spectrum Disorders-Heterogeneity Approach Rather Than Diagnostic Boundary

Complex diseases such as schizophrenia and autism are heterogeneous in clinical presentation and etiology. This high heterogeneity constitutes the challenges for the clinical diagnosis and etiological research, resulting in that the majority of research findings cannot be replicated in the independent samples. For the high comorbid rate between the diagnoses of schizophrenia and autism spectrum disorders (ASD), and the shared neurocognitive deficits, genetic risks, and biological markers between the two disorders, a heterogeneity approach may probably be more promising than to arbitrarily split the two diagnostic categories apart or lump them together for etiological research. In schizophrenia, patients with a very early onset of disease and with preceding neurodevelopmental conditions may imply a different underlying etiology from those with typical onset and without neurodevelopmental conditions. Echoing the evidence that in early onset Parkinson's disease, PARK2 (encoding parkin protein) mutations are successfully reported to be as frequent as 49% with an autosomal-recessive mode of inheritance , representing a specific disease entity of Parkinson's disease. Therefore, it is critical to characterize the clinical phenotypes for this subpopulation of very early onset patients, including their clinical manifestation, disease course, and treatment response, as well as early developmental history and morphological characteristics. These may establish an important base for investigating the etiology and providing adequate clinical care for the heterogeneous syndrome of schizophrenia