Introduction

The term manic-depressive psychosis was introduced in 1896 by Kraepelin. Mania and depression had already been described as stages of a single morbid process, but Kraepelin’s observations and his clearly formulated conception of the disease constituted a definite advance. Since then a great number of scientific investigations on this psychosis have been carried out. Although our knowledge of the disease is still incomplete and the conception of it varies, it is recognized all over the world as an entity. As far as we know, cases of manic-depressive psychosis occur in all parts of the world. Clear and important differences between different nations and different races have not been shown to exist. The studies of the frequency of the disease in the general population of different countries agree fairly well. Investigations on the heredity of manic-depressive psychosis may also be considered to agree rather closely. It is true that these studies have not been made with a uniform method, so it is not easy to compare all of them, and a detailed discussion of the results is thus in many cases of no great use. The research on manic-depressive psychosis may, however, fairly be said to point to the great importance of genetic factors in the causation of the disease. Cases of manic-depressive psychosis have frequently been found to occur in successive generations. Many psychiatric investigations on the importance of hereditary factors have treated only the general “neuropathic .taint”, considering all mental illnesses and abnormalities together, and sometimes even the organic nervous diseases. Very early attempts were made, however, to treat different states separately, which is certainly the only way of gaining insight into these states. Vogt (1910) made a study of the heredity of manic-depressive psychosis which was very good, considering the relatively slight knowledge of genetics and of manic-depressive psychosis a t that time. He examined 108 probands and their relatives. Since age-distributions were not included, it is npt possible to calculate morbidity risks. 20 of the parents had certain or uncertain manic-depressive psychosis, i. e. about 10 yo. The author concluded that manic-depressive psychosis “may be inherited as such”, but that the disease has no connection with other mental diseases or abnormalities from a genetic point of view. Vogt found a great number of suicides in his material.