[Inborn or acquired? The assertions and methods of twin research in psychiatry].

Is Insanity inborn or acquired?--This question has become more actual in the last years as a consequence of progresses of psychotherapeutic and genetic research and the movement of antipsychiatry. This paper tries to clarify the dignity of the study of twins as contribution to an answer to this question. Some genetic terms are explicated as genotype, phenotype, monofactoriel and multifactoriel genetic transmission with sill. The significance of twin studies, of its contribution to the calculation of heritability and detection of environmental factors, and methodical problems as determination of zygosity and concordance, sampling method and correction of age are critically discussed.