Adoption studies on psychiatric illness : epidemiological, environmental and genetic aspects

Abstract: The aim of this study is to evaluate the outcome of adoptions and to study the gene-environment influences on psychiatric illness as well as sick-leave patterns. The material consists of 2 966 adopted persons born between 1917 and 1949, their 5 932 adoptive parents and 5 438 identified biological parents.Adopted persons had a higher incidence of personality disorders and substance abuse than non-adopted controls. Adopted men also had an increased incidence of neuroses. Adopted women had an increased sick-leave because of somatic complaints, especially upper respiratory tract infections and abdominal complaints of short duration. Somatization i.e. more than 2 sick-leaves/year because of somatic complaint together with nervous complaints was more frequent among adopted women. Women with somatization could be separated into 2 types according to the pattern of sick-leave. Type 1 ("high frequency") had frequent sick-leaves for psychiatric, abdominal and back complaints. They also had a high frequency of alcohol abuse. Type 2 ("diversiform") had more diverse complaints and had fewer sick-leaves because of nervous complaints.High frequency somatizers had biological fathers with teenage onset of criminality and frequent registrations for alcohol abuse. Diversiform somatizers had the same genetic background as adopted men with petty criminality or male limited alcoholism.No specific genetic influences on treated depression or substance abuse were found in this study. However, a non-specific vulnerability of the biological mother influenced on the risk of depression and substance abuse among adopted women.There were some indications that placement in the adoptive home between 6 and 12 months of age was associated with reactive neurotic depression in adult life. Otherwise early negative experiences in term of unstable placements before adoption did not significantly influence on psychiatric illness in adulthood.Affective disorders in the adoptive father were associated with treatment for depressions or substance abuse in the adoptee. Low social status in the part of the adoptive father increased the risk of somatization of both types in the adoptee.