Disorders of the CNS are broadly categorized as either psychiatric or neurodegenerative with a major degree of overlap in symptoms. Thus neurodegenerative disorders also have a high incidence of psychiatric comorbities including anxiety and depression. Psychiatric disease includes a variety of disorders such as schizophrenia, depression, obsessive compulsive disorder (OCD), attention deficit hyperactivity disorder (ADHD), and others. The underlying pathology is usually considered to be the result of synaptic dysfunction driven by: (1) a dysregulation of neurotransmitter availability or (2) signaling, the latter at the receptor and/or signal transduction levels. The net result is an alteration in neuronal circuitry involving multiple neurotransmitter/neuromodulator systems.
Neurodegenerative disease involves a defined degenerative process in which neurons are lost either by necrosis or apopotosis. This category is typified by slow chronic disorders that include Parkinson's disease and AD, but also includes more acute cell loss due to traumatic insults including stroke (brain attack) and spinal or brain damage. There are major issues with diagnosis in the absence of robust biomarkers.6 For example, there are cases where the AD disease phenotype is predominant and where the diagnosis of AD has not been supported by autopsy.
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