Hermann Hoffmann's 1921 Monograph: "The Offspring of Endogenous Psychoses: Genealogical-Characterological Examinations".

Five years after the publication of Rüdin's major sibling study, Hermann Hoffmann, working with Rüdin, performed the first systematic study of the risk for dementia praecox (DP) in offspring of DP probands. Field work was limited to 3 months. Hoffmann ascertained families with at least one parent with certain DP, after Kraepelin, with children the youngest of whom were at least 30 years old. These families contained 103 offspring 30 years or older of whom 7 had definite DP and two possible DP for an estimated risk of 6.8%-8.7%. Hoffmann assessed schizoidia in these children, reporting the quite high risk figure of 47.6%. Hoffmann explored a wide range of two and three locus recessive models in his modest sample. He finds Rüdin's two locus recessive model at the boundary of his results and then reviews three additional more complex models. The simplest is a three-locus recessive model which fits his data better. He also explores an oligogenic three locus model with risk classes of individuals with 1 to 6 risk alleles and an epistatic model where two loci form a di-recessive model for schizoidia, and the third locus is a dominant required for the expression of psychosis. Hoffman questioned whether DP was a "unit-character" appropriate for Mendelian analysis and advocated for a much larger study of offspring. His work should be appreciated in light of his enthusiastic endorsement of Nazi eugenic goals.