Henri Legrand du Saulle's 1873 book: "La Folie Héréditaire" (hereditary madness).

In his 1873 monograph "La Folie Héréditaire," the French Alienist Legrand du Saulle (LdS) first outlined his understanding of hereditary factors in insanity and then described in detail the theory of Hereditary Madness (HM) that emerged from the writings of his mentor Bénédict Morel. This form of insanity was thought to arise only in families with neuropathic traits. Degeneration theory, proposed by Morel, postulated a within-family "evolution" of increasingly severe psychopathology, typically beginning with mild neuropathic traits and associated idiosyncrasies, and progressing over generations to hereditary madness, mental retardation, epilepsy, and eventual sterility. LdS took strong positions in favor of (i) the heterogeneous transmission of mental illness within families, (ii) consideration of both direct and collateral relatives, and (iii) the inheritance of a predisposition to illness, not the illness itself. He carefully examined the wide range of psychopathology and physical stigmata that occurred in what he called "inheritors" of the neuropathic trait. A unique feature of his work was the use of familial patterns of psychopathology to define a psychiatric disorder. While the theory of HM did not gain wide popularity outside of 19th century France, the concept of neuropathic traits was used extensively in early 20th century psychiatric genetics.