Schizophrenia and bipolar disorder: The road from similarities and clinical heterogeneity to neurobiological types

• Schizophrenia and Bipolar Disorder are prevalent and disabling mental disorders.
• There is considerable clinical heterogeneity within each of the two disorders.
• To date there is no biomarker which is specific for either of the disorders.
• Combining the clinical and the biomarker based approach will improve diagnostic algorithms.
• This would lead to a better treatment choices and more favorable outcomes

Although diagnosis is a central issue in medical care, in psychiatry its value is still controversial. The function of diagnosis is to indicate treatments and to help clinicians take better care of patients. The fundamental role of diagnosis is to predict outcome and prognosis. To date serious concern persists regarding the clinical utility and predictive validity of the diagnosis system in psychiatry, which is at the most syndromal. Schizophrenia and bipolar disorder, which nosologists consider two distinct disorders, are the most discussed psychiatric illnesses. Recent findings in different fields of psychiatric research, such as neuroimaging, neuropathology, neuroimmunology, neuropsychology and genetics, have led to other conceptualizations. Individuals with schizophrenia or bipolar disorder vary greatly with regard to symptoms, illness course, treatment response, cognitive and functional impairment and biological correlates. In fact, it is possible to find heterogeneous correlates even within the same syndrome, i.e., from one stage of the disorder to another. Thus, it is possible to identify different subsyndromes, which share some clinical and neurobiological characteristics. The main goal of modern psychiatry is to ovethrow these barriers and to obtain a better understanding of the biological profiles underlying heterogeneous clinical features and thus reduce the variance and lead to a homogeneous definition. The translational research model, which connects the basic neuroscience research field with clinical experience in psychiatry, aims to investigate different neurobiological features of syndromes and of the shared neurobiological features between two syndromes. In fact, this approach should help us to better understand the neurobiological pathways underlying clinical entities, and even to distinguish different, more homogeneous, diagnostic subtypes.