[Biological risk factors in depression]

Various biological abnormalities have been reported in depressed patients. They concerned: Monoamines, assessed by measuring neurotransmitters precursors, catabolites, activity of synthesis and catabolism enzymes, uptake and release velocity. Membrane structure and physiology via receptors and transmembrane. Ionic changes. Neuroendocrine systems. Biological rhythms. Abnormalities are inconsistent and varied. No coherent theory of depression can account for these abnormalities: no biological measure can be considered as a specific marker. It is important to look for non specific factors of variation of these indices. Overall it is difficult to determine whether a reported biological abnormality can be considered as a cause or a consequence of the clinical feature. A vista for future research may be the availability of new investigation techniques as brain imaging and molecular genetics.