“Medical Genetics in the 19th Century As Background to the Development of Psychiatric Genetics”, 2022-07-02 ():
This article examines the relationship between the early efforts of alienists to understand the role of heredity in the etiology of insanity in the 19th century and the parallel efforts of the nascent discipline of medical genetics.
I review 3 monographs on general medical genetics: Adams in 1814, Julius Henry Steinau in 1843, and Robert Alexander Douglas Lithgow in 1889.
Numerous parallels were seen between their writings and those of their contemporary alienists working on mental disorders including (1) an emphasis on the transmission of the liability to illness rather than the illness itself, (2) discussions of the homogeneous versus heterogeneous nature of familial transmission of disease, (3) the relative value of direct versus indirect hereditary effects, (4) the role of mothers versus fathers in transmitting liability, (5) possible environmental sources of familial clustering, and (6) the transmission of age at onset of illness. All 3 medical genetic authors noted that insanity was among the more heritable of human disorders. Furthermore, Lithgow noted the importance of heritable influences on the non-psychotic forms of psychiatric illness rarely seen in asylums.
This survey demonstrates substantial consilience in the topics of interest and conclusions of the nascent general medical and psychiatric genetics’ communities in the 19th century.
…Our 19th-century medical geneticists were very interested in the nature of the familial transmission of biomedical conditions and especially the differences between the transmission of a disorder versus the susceptibility to that disorder. For most conditions, they concluded that susceptibility to disease was what children inherited from their parents. We saw some disagreement among our medical genetics authors in the ways they conceptualized that. Adams gave names to 2 levels of diseases liability: disposition and predisposition. Neither Steinau nor Lithgow adopted that particular terminology, but all 3 clearly agreed on the general concept—that disease most typically arose when individuals at genetic risk experienced some kind of exciting cause, typically from the environment. The interest in the nature of hereditary transmission was also prominent in many of those writing on psychiatric genetics in this century, from authors as diverse as Spurzheim, Nobel, Morel, and Kraepelin (2021c). As in medical diseases, they favored the hypothesis of a transmitted liability in part because of the common observation that insanity often skip generations or affects only one among a number of siblings (2021c).
…A major theme for psychiatric geneticists of the 19th century was whether the nature of the transmission of mental illness within families was homogeneous (“like transmitting like”) or heterogeneous—that is relatives of insane patients suffering from a wide range of psychiatric disorders…Those working in the genetics of psychiatric illness in the 19th and early 20th century debated whether the sole focus should be on parent-offspring transmission (ie. direct heredity) or whether collateral relatives (ie. indirect heredity) should also be considered, especially when deciding whether an admitted asylum patient did or did not have a “hereditary load.”…Concerned with distinguishing different sources of familial aggregation, our medical authors considered factors other than inheritance, separating out disorders they considered familial but not hereditary…Steinau also raised the hypothesis that age at onset for many medical diseases appears to be inherited… All 3 of our authors saw madness as a paradigmatic example of a disorder with strong heritable influences.