Signature Response to Light Therapy in Unipolar and Bipolar Major Depressive Episode (MDE)

Major depressive episode (MDE) are severe and common psychiatric disorders that affect up to 20% of the general population. MDE cause a decrease in psychosocial functioning, quality of life, and is associated with a high rate of suicides. They will be the leading cause of disability by 2030 according to the World Health Organization. The international effort carried out to identify biomarkers of MDE has been hampered by the heterogenous nature of MDE (unipolar, bipolar, seasonal, non-seasonal) and their heterogeneous response to treatment. Response rate to antidepressant drugs is only 40 to 50%, leading to the use of drug combinations and development of alternative therapeutics such as light therapy (LT). It was demonstrated that LT, as a first line treatment of MDE with and without seasonal pattern (± SP), has comparable efficacy to antidepressants. LT has the advantage of being also effective in improving both sleep, alertness and circadian rhythms, which may be altered in depression, contrary to antidepressant drugs that target mainly mood. Further research is warranted to determine the most efficient lighting parameters to use depending on depression characteristics, as well as to identify signature biomarkers of response. Besides, no studies have directly evaluated both subjective and objective biomarkers of sleep, wake, biological rhythms, and light signalling pathways and activation in patients with MDE ± SP. The main objective of the research will be to identify the signature of response to LT examining the correlation between the measures of biological and clinical parameters before LT and their evolution at the end of the procedure, and the therapeutic response. The primary endpoint of the study will be the therapeutic response to LT measured by the difference of MADRS score between Visit 1 and Visit 4 (end of the therapeutic protocol). Therapeutic response to LT considered as a success will be defined as at least a 50% reduction of MADRS score between th