Psychiatric genetics is basically a research program with no connection to treatment except for very rare high impact genetic loci.
An endophenotype refers to a characteristic that is not easily observed on the surface. Almost all mental illnesses are due to epigenetic dysregulations. The endophenotypes of psychiatric illnesses would be the sets of epigenetic marks that are associated with given mental illnesses. The variability in symptoms in given illnesses is due to variations on the basic sets of epigenetic marks associated with such illnesses.
Mental illnesses arise due to dysregulation of TET enzymes and JmnjC-domain containing .proteins with TET enzymes involved in DNA demethylation and JmnjC-domain containing proteins involved in histone demethylation. Histone acetylation which requires acetyl-coenzyme A also plays a part.
Though dysregulation of TET enzymes and JmnjC-domain proteins and dysregulation of acetyl-coenzyme A are fundamental to all mental illnesses various mental illnesses separate from each other as spatially closely associated pathways fall together. Use the pathways or lose the pathways. And as these are epigenetic dysregulations, pathways that are lost are spatially localized to various organs and/or regions of organs, for example, regions of the brain. Trying to distinguish mental illnesses by examining genes is pointless.
Trying to isolate endophenotypes so as to enhance treatments is not necessary. With basic epigenetic dysregulations addressed almost all mental illnesses. can be treated. A treatment that addresses dysregulation of TET enzymes and JmnjC-domain proteins and dysregulation of acetyl-coenzyme A could address all mental illnesses.