C. Robert Cloninger - Stockholm Adoption Study

Stockholm Adoption Study

The answer to the need for better data about separation experiments came in the form of a long-term collaboration between Cloninger and Michael Bohman, the head of child psychiatry at the University of Umea in Sweden. Bohman had read some of Cloninger's papers on the analysis of separation experiments and asked for Cloninger's assistance in his own research. For several years, Bohman had been studying the behavior of a large birth cohort of children born in Stockholm. The children had been separated from their biological parents at birth and reared in adopted homes. Extensive data about alcohol abuse, criminality, and physical and mental complaints to physicians were available in Sweden as a result of the extensive health and social records for all people in the country. Cloninger developed methods for what he called a "cross-fostering" analysis. Information about the genetic background of adoptees was measured by data about their biological parents. Information about their rearing environment was measured by data about their adoptive parents and home environment. This permitted study of the independent contributions of the genetic and environmental backgrounds independently and in combination in a sample of thousands of adoptees. Their first joint paper on a cross-fostering analysis of the inheritance of alcoholism in men became an ISI Science Citation Classic that convinced most scientists that vulnerability to alcoholism was genetically heritable in part.

Cloninger, Bohman, and Soren Sigvardson distinguished two subtypes of alcoholism that differed in their clinical features and pattern of inheritance: type 1, associated with anxiety proneness and loss of control over alcohol intake after age 25; and type 2, associated with impulsivity and antisocial behavior before age 25. Cloninger proposed that the differences between these two groups of people were explained by personality traits that were observable in childhood, long before any exposure to alcohol. He confirmed this by measuring the personality of boys when they were in the fourth grade, about 10 years of age, based on detailed interviews with their teachers and without any knowledge of their drinking status as adults. The personality ratings of Cloninger were based on his tridimensional model of temperament. The personality model also helped the team to understand other findings they obtained about the inheritance of criminal behavior, somatization (i.e., many physical complaints), anxiety, and depressive disorders. The original findings were later confirmed by a replication study using the same methods conducted in Gothenburg, Sweden. Overall, these adoption studies provided strong evidence for the contribution of both genetic and environmental influences on vulnerability to alcoholism, somatization, criminality, anxiety, and depressive disorders.