What is "endophenotype"

n. (context medicine English) any hereditary characteristic that is normally associated with some condition but is not a direct symptom of that condition.

Endophenotype is a genetic epidemiology term which is used to separate behavioral symptoms into more stable phenotypes with a clear genetic connection. The concept was coined by Bernard John and Kenneth R. Lewis in a 1966 paper attempting to explain the geographic distribution of grasshoppers. They claimed that the particular geographic distribution could not be explained by the obvious and external "exophenotype" of the grasshoppers, but instead must be explained by their microscopic and internal "endophenotype."

The next major use of the term was in psychiatric genetics, to bridge the gap between high-level symptom presentation and low-level genetic variability, such as single nucleotide polymorphisms. It is therefore more applicable to more heritable disorders, such as bipolar disorder and schizophrenia. Since then, the concept has expanded to many other fields, such as the study of ADHD, addiction, Alzheimer's disease obesity and cystic fibrosis. Some other terms which have a similar meaning but do not stress the genetic connection as highly are "intermediate phenotype", " biological marker", "subclinical trait", "vulnerability marker", and "cognitive marker". The strength of an endophenotype is its ability to differentiate between potential diagnoses that present with similar symptoms.