Neurocognitive performance as an endophenotype for bipolar disorder

Identification of the underlying liability to develop bipolar disorders (BD) is hindered by the genetic complexity and phenotypic heterogeneity of the disease. The use of endophenotypes has been acknowledged as a promising approach that may detect the hidden manifestations of a genetic liability for an illness. One of the most commonly proposed endophenotypes in BD is neurocognitive performance. We identified and examined previously published review articles that had any data pertaining to endophenotypes in BD and combined this with an extensive review of studies of cognitive deficits in BD from 2000 onwards. Using criteria for a valid endophenotype, we identifed that the domains of executive functioning and verbal memory are the most promising candidate endophenotypes for BD. However, they do not meet the criteria for specificity as similar deficits present in schizophrenia and/or severe or psychotic major depressions. Further research is needed as the findings regarding endophenotypes show between-study heterogeneity. In the future, examination of quantitative traits may offer a more promising approach to the study of endophenotypes rather than solely focusing on diagnostic categories.