Rüdin's Unpublished Family Study From the Early 1920s: “On the Inheritance of Manic‐Depressive Insanity”

ABSTRACT Ernst Rüdin, an important and controversial figure in the history of psychiatric genetics, published only one major empirical study on siblings of dementia praecox (DP) probands in 1916. He conducted a parallel study of siblings of probands with manic‐depressive insanity (MDI), but the resulting monograph, written in the early 1920s, was left incomplete and unpublished. We translated this monograph and here summarize its main findings. The morbid risk for MDI in the siblings of MDI probands with unaffected parents was 7.47%, inconsistent with simple Mendelian models. Working with his data, Weinberg proposed a complex trimeric dominant‐recessive Mendelian model for MDI. He also presented several innovative analyses to our knowledge without precedent in prior studies. First, over a 16‐year follow‐up, a proportion of his proband sample developed DP. The risk for DP and MDI in siblings of those “converted” cases closely resembled risks seen in siblings of definitive DP and not definitive MDI probands. Second, knowing the familial psychopathology of his probands, Rüdin, concerned about his objectivity, asked a colleague to provide the diagnoses blind to the fa