Characterisation of age and polarity at onset in bipolar disorder. - Kalman JL; Olde Loohuis LM; Vreeker A; McQuillin A; Stahl EA; Ruderfer D; Grigoroiu-Serbanescu M; Panagiotaropoulou G; Ripke S; Bigdeli TB; Stein F; Meller T; et al. (The British journal of psychiatry : the journal of mental science, 2021)