Eugen Bleuler's Views on the Genetics of Schizophrenia in 1917

In 1917, Eugen Bleuler published an article (Mendelismus bei Psychosen, speziell bei der Schizophrenie [Mendelism in the Psychoses, especially Schizophrenia]) in response to the recently published first systematic family study of dementia praecox (DP) by Ernst Rüdin, then working under Kraepelin in Munich. Although briefly commented upon by David Rosenthal in 1978, this article has never been thoroughly reviewed or translated. Of the many themes addressed, four are especially noteworthy. First, Bleuler argues that understanding the transmission patterns of schizophrenia in families requires definitive knowledge about the boundaries of the phenotype which he argues are unknown. Rüdin's choice-Kraepelin's concept of DP-is, he asserts, too narrow. Clarifying the genetics of schizophrenia is inextricably bound up with the problem of defining the phenotype. Second, Bleuler argues for the importance of "erbschizose" (literally "inherited schizoidia") wondering whether his "4 As" or other "brain-anatomical, chemical, [or] neurological characteristics" might underlie the genetic transmission of schizophrenia. Third, Bleuler was deeply interested in the nature of the onset of schizophrenia, suggesting that environmental adversity could provoke "latent illness to become manifest." It was important, he argued, to identify such risk factors and incorporate them into genetic models. Fourth, although not optimistic that current knowledge would permit a resolution of the transmission model for schizophrenia, he finds single-locus models implausible and at several points wonders whether polygenic models might better apply. A complete translation of the article is provided.