The Endophenotypic Involvement of Neuroticism, REM Sleep Abnormalities, and Cognitive Deficits in Depression and Schizophrenia.

Abstract

While genes refer to the bases that encode our phenotypes, a phenotype often refers to observable characteristics, such as hair color, eye color, or height. However, a common mistake is overgeneralizing phenotypes to solely equate to an outward appearance rather than having any merit at a genetic level. In neuroscience, phenotypes bridge the genetic information underlying neurocognitive disorders. Neuronal phenotypes, or endophenotypes, link measurable traits and genetic mutations. As intermediate traits between a psychiatric disorder's genetic level and physical presentation, researchers can now efficiently identify the associated genes and defined characteristics. Notably, two common neuropsychiatric disorders, depression and schizophrenia, share overlapping endophenotypes: neuroticism, REM sleep abnormalities, and neurocognitive deficits. Firstly, neuroticism has earned itself a spot amongst psychology's "Big 5" personality traits, in which it presents itself as an individual's tendency to spiral into anxious and depressive habits. These neurotic tendencies additionally act as genetic predictors for the future onset of schizophrenia. Secondly, REM sleep abnormalities act as biological markers for schizophrenia due to shorter sleep latency and increased REM density correlating with severe schizophrenic symptoms. These abnormalities are not limited to schizophrenia, though, as REM sleep alterations also relate to depression due to disruptions in the neurotransmitters responsible for REM sleep. Finally, cognitive control deficits impact an individual's ability to achieve goals by impeding focus and fluidity between tasks, traits associated with both depressive and schizophrenic behavior. The purpose of this study was to provide an in-depth analysis of the leading genetic markers within both depression and schizophrenia. This study hypothesizes that neuroticism, REM sleep abnormalities, and cognitive deficits are foundational to both depression and schizophrenia despite each endophenotype having their respective impacts on each disorder.