Importance Genetic factors contribute to risk for bipolar disorder (BP), but its pathogenesis remains poorly understood. A focus on measuring multisystem quantitative traits that may be components of BP psychopathology may enable genetic dissection of this complex disorder, and investigation of extended pedigrees from genetically isolated populations may facilitate the detection of specific genetic variants that affect BP as well as its component phenotypes. Objective To identify quantitative neurocognitive, temperament-related, and neuroanatomical phenotypes that appear heritable and associated with severe BP (bipolar I disorder [BP-I]) and therefore suitable for genetic linkage and association studies aimed at identifying variants contributing to BP-I risk.

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No question in psychiatric nosology has attracted such consistent controversy over the past several generations as the setting of the boundary between schizophrenia and major mood disorders. Indeed, Kraepelin, the originator of this diagnostic distinction, was well aware of the difficulties of defining precisely this boundary. A closely related question has been whether there exists, between these 2 pivotal diagnostic entities, a third valid disorder that shares some clinical features with each: schizoaffective disorder (SAD)

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