Bruno Schulz's 1930 article "The Hereditary Relationships of Old-Age Paranoid Psychosis".

In the 1899 6th edition of his influential textbook, Kraepelin proposed a diagnostic category of "Old-Age Paranoid Psychosis." In this 1930 article, Bruno Schulz studied the morbid risk (MR) of several disorders and traits in the parents, siblings, offspring, and nieces/nephews of 51 probands with "Old-Age Paranoid Psychosis." His results permitted an evaluation of the validity of Kraepelin's category of Old-Age Paranoid Psychosis, in particular, whether it was a form of psychosis resulting from "senile changes" or late-onset schizophrenia. The MR of schizophrenia in these four groups of relatives varied from 0 to 2.4% with 3 of 4 somewhat higher than population expectations but much lower than parallel results in relatives of schizophrenics. By contrast, the rates of eccentricity in these relatives were uniformly elevated over population rates, sometimes approaching those seen in relatives of schizophrenics. Schulz concluded, from his study, that Old-Age Paranoid Psychosis was a distinct disorder not closely related to schizophrenia. However, he suggested that a family history and/or a premorbid trait of eccentricity increases the risk of developing a paranoid psychosis in old age, particularly when associated with physical or mental decline. He was uncertain about whether the trait of eccentricity he found in this study was very similar or distinct from that observed in excess in relatives of schizophrenics. This study was the first, to the best of our knowledge, to use a family study design explicitly to address a nosologic question-in this case the familial relationship between Old-Age Paranoid Psychosis and schizophrenia.