[Biological psychiatry and current classifications of depressive disorders]

By means of a review of genetic, biological and neurophysiological studies, we attempted to validate the DSM III-R depressive disorder categories. Genetic studies support the distinction between bipolar and recurrent major (unipolar) depression although genetic heterogeneity and variable phenotypic expressivity have been suggested in bipolar depression. Biological and neuroendocrine abnormalities in depression seem to relate more to a particular symptomatological profile than to a specific depressive subtype including the bipolar-unipolar dichotomy. For example, catecholamines and serotonin metabolism seem to reflect respectively psychomotor status and aggressiveness in depression. Using genetic and biological criteria, major depression with psychotic features is the best validated category of the four main DSM-R major depressive subclasses or specifications (psychotic, chronic, melancholic, seasonal). Psychotic depression seems to constitute the most coherent subgroup and biological abnormalities such as dexamethasone non suppression and shortened REM latency are very often observed. An important confounding variable in these biological validation studies is the severity of the depressive state. Psychotic depression is considered to be a more severe depressive subtype and also shows marked biological disturbances. Conversely, in seasonal depression, a less severe depressive subtype, CSF monoamine metabolism abnormalities, dexamethasone non suppression and shortened REM latency could not clearly be demonstrated. Genetic studies show that early onset dysthymia and cyclothymia could be part of the affective spectrum and some maintain that these two clinical entities are attenued forms of bipolar or recurrent major depression.