Major depression (MD) is a major public health problem worldwide. Nevertheless, its pathophysiology remains unclear and no specific biological marker has been associated to the disease so far.

To investigate whether such marker(s) exist(s), we collected peripheral blood mononuclear cells (PBMC) from a restricted cohort of MD inpatients at two different time points: at the time of major depressive episode with melancolic features and 8 weeks later (median score on the Hamilton Depression Rating Scale were 38 and 14.5 (p<0.05), respectively). We also collected PBMC from age and sex-matched control individuals. Total RNAs were extracted and we studied the mRNA level alterations of 83 candidate genes by qRT-PCR using the TaqMan Low Density Array technology.

When compared to control samples, a significant down- and up-regulation of mRNA level was observed for numerous genes involved in MD. Remarkably, while the transcription level of these genes was heterogeneous within both controls and patients, 8 weeks after the major depressive episode, it was very homogeneous during the acute phase of the disease. Furthermore, some mRNA level variations were statistically correlated to the clinical severity of the symptomatology during the acute phase.

Thus, we conclude that some mRNA level alterations provide a good signature of the MD state.