Endophenotype

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Endophenotype is a psychiatric concept and a special kind of biomarker. The purpose of the concept is to divide behavioural symptoms into more stable phenotypes with a clear genetic connection. The concept was originally borrowed by Gottesman & Shields from insect biology.

They make five demands a biomarker or cognitive marker must fulfill to be called an endophenotype:

1. The endophenotype is associated with illness in the population.
2. The endophenotype is heritable.
3. The endophenotype is primarily state-independent (manifests in an individual whether or not illness is active).
4. Within families, endophenotype and illness co-segregate. Subsequently, an additional criterion that may be useful for identifying endophenotypes of diseases that display complex inheritance patterns was suggested.
5. The endophenotype found in affected family members is found in nonaffected family members at a higher rate than in the general population.

In the case of schizophrenia, the overt symptom could be a psychosis, but the underlying phenotypes are, for example, a lack of sensory gating and a decline in working memory. Both of these traits have a clear genetic component and can thus be called endophenotypes.

Other terms with similar meaning but not stressing the genetic connection are “intermediate phenotype,” “biological marker,” “subclinical trait,” “vulnerability marker,” and "cognitive marker".

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