The initial sample consisted of euthymic patients with BD type I, II or not otherwise specified (NOS) who were recruited from three psychiatric departments in France (Paris/Créteil, Bordeaux and Nancy). Patient inclusion criteria were: aged over 18 years; having a diagnosis of BD according to DSM-IV criteria18; being Caucasian; and clinically normothymic at the time of inclusion (i.e. having a Montgomery Asberg Depression Rating Scale score19 and a Mania Rating Scale score20 below five as well as no major mood episodes in the last three months). Patients were interviewed using the French version of the Diagnostic Interview for Genetic Studies (DIGS)21, providing lifetime DSM-IV axis I diagnoses18. The AAO of BD was determined retrospectively and was defined as the age at which a patient first met DSM-IV criteria for a major depressive or (hypo)manic episode according to clinical information collected with the DIGS. This sample was a subsample of the one published in 2013 that included 418 patients from France and 169 patients from Norway13. For this study, only patients from France were included and the inclusion was based only
