The Core Phenotype
As briefly mentioned in the section “From Trait to Treatment (click here to go to that section) the Core Phenotype is the name given to the profile that emerged from the dimensional analysis of data from over 3,000 Child Bipolar Questionnaires (CBQ) submitted for children at risk for, or with a community-based diagnosis of bipolar disorder. The proposal of the phenotype is strengthened by the fact that one of its dimensions, the fear-of-harm dimension, is highly heritable.
The set of ten dimensions that resulted from the analysis provide a new perspective of a single syndrome as experienced by the 3,000 children whose data was examined. The ten dimensions, and the symptoms and behaviors that make up those dimensions can be viewed by clicking here.
While the ten dimensions together may provide a comprehensive description of the condition, they are unwieldy to use for diagnostic purposes. Towards that end, investigators went back to the CBQ and determined exactly which symptoms from the CBQ most correlated with the fear-of-harm trait itself. They arrived at a list of 22 symptoms which satisfy this goal and which they call the Core Index.
CBQ Core Index Subscale
These 22 CBQ items are an excellent means to determine the presence of the fear-of-harm trait. If one fills out the CBQ, an algorithm will indicate the Core Index score. A study showed that the Core Index has excellent agreement with the Kiddie-Schedule of Affective Disorders and Schizophrenia (K-SADS). The K-SADS is a clinical interview that is currently considered the gold standard by which a diagnosis of bipolar disorder in children is made. In fact, the Core Index outperformed the DSM definition to predict the diagnosis.
This information is presented in detail in articles published in The Journal of Affective Disorders as linked below:
A strategy for identifying phenotypic subtypes- Concordance of symptom dimensions between sibling pairs who met screening criteria for a genetic linkage study of childhood-onset bipolar disorder using the Child Bipolar Questionnaire