The concept of the endophenotype was introduced to psychiatry over 30 years ago by Gottesman & Shields (1973), but its popularity is more recent: there are eight PubMed entries before 2000 compared to 150 in the current century. Gottesman & Shields (1973) adapted the term from a 1966 paper that attributed the geographical distribution of grasshoppers to the insects’ ‘endophenotype’ (John & Lewis, 1966), a neologism alluding to a phenotype that was microscopic and internal, and therefore obscure to casual observation. Endophenotypes in psychiatry retain the notion of an internal process, but one that can be objectively measured, ideally in a robust and reliable fashion, a characteristic often lacking in the diseases with which they are associated.
