LETTER TO THE EDITOR Open Access

Circadian biomarkers in patients with bipolar disorder: promising putative predictors of lithium response Pierre Alexis Geoffroy1,2,3,4*, Bruno Etain4,5,6, Sarah Sportiche1,2,3,4 and Frank Bellivier1,2,3,4 Bipolar disorder (BD) is a common, severe mental disorder with a high recurrence rate. Lithium (Li) is the cornerstone of BD treatments to reduce recurrence, suicide, and mortality risks. However, only 30 % of patients treated with Li achieve complete remission, and few markers of the response to treatment have yet been identified for application in routine practice. Circadian biomarkers may be relevant predictors of individual responses to Li because (1) Li has been shown to affect circadian rhythms, (2) disrupted circadian rhythms are a core expression of susceptibility to BD, and (3) circadian abnormalities during euthymia are associated with relapses