Biomedical subjects
Publications and source records attributed to S Torgersen.
One hundred and fifty anxiety neurotic and neurotic depressive twin probands were differentiated into three groups by means of discriminant analysis, 50 in each group. The groups were named: pure anxiety neurosis, mixed anxiety-depression, and pure neurotic depression. Analysis of concordance rates indicated that only pure anxiety neurosis seemed to be influenced by hereditary factors.
The aim of this study was to investigate etiological and nosological aspects of the schizotypal and borderline personality disorders. The sample consisted of 44 schizotypal, 15 schizotypal and borderline, and ten borderline same-sexed twin probands. The investigation of the co-twins indicated that genetic factors seemed to influence the development of the schizotypal, but not the borderline, personality disorders. The basic genetic core of the schizotypal syndrome seemed to consist of schizoid and paranoidlike features, and not psychoticlike cognitive and perceptual distortions. The study did not indicate any relationship between schizotypal and borderline personality disorders and affective and schizophrenic disorders. Further research is needed to confirm the independent status of the schizotypal syndrome in relation to the schizoid, avoidant, and paranoid personality disorders, and the borderline syndrome in relation to the histrionic , narcissistic, and antisocial personality disorders.
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We investigated genetic factors in the determination of anxiety disorders in a study of 32 monozygotic (MZ) and 53 dizygotic (DZ) adult same-sexed twins. The frequency of anxiety disorders was twice as high in MZ as in DZ co-twins of the total proband group, alike in the MZ and DZ co-twins of the generalized anxiety disorder proband group, and three times as high in MZ as in DZ co-twins of the other proband groups. Anxiety disorders with panic attacks were more than five times as frequent in MZ as in DZ co-twins in a combined group of probands with panic disorders and agoraphobia with panic attacks. For generalized anxiety disorder, genetic factors were not apparent, while genetic factors were not apparent, while genetic factors appear to influence the development of the other anxiety disorders, especially panic disorder and agoraphobia with panic attacks.
In a study of 229 neurotic same-sex adult twins admitted to all psychiatric in- and out-patient clinics and mental hospitals in Norway, a statistically significant, moderately higher concordance was found for MZ than for DZ twins. When the sample was subdivided, this higher concordance for MZ pairs was true only for male twins and for twins admitted to mental hospitals. The results are compared to those from earlier studies; different findings on the importance of genetic factors in the development of neuroses may be due to differences in sample selection.
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Lazare et al have demonstrated a factor structure similar to the oral, obsessive, and hysterical personality syndromes in a female patient population. The factor structure has been replicated in a sample of 99 predominantly "normal" females and male twin pairs. Furthermore, it was found that hysterical traits in female subjects and oral traits in male subjects seemed to have a genetic component. The study also indicated that environmental factors from an early age influence the development of the personality structure.
The inheritance of General Neurotic, Obsessive, and Impulsive Hysterical personality traits has been studied in a sampling of 260 female and male adult same-sexed twins. At least one of the twins in each pair had been treated for neurotic or borderline disorders. The results showed that the General neurotic and the obsessive personality factor had a significantly but moderately high hereditary component. The same was also true for more than half of the 17 separate personality scales. No personality scales emerged as highly hereditary. Therefore, each item was analyzed separately, and items classified as either distinctly hereditary or environmental were placed in each of these two groups. The items of the two groups were separately factor-analyzed, and three hereditary and three environmental main factors emerged. The hereditary factors seemed to represent a basic core in the three personality factors of the total questionnaire, whereas the environmental factors could be explained as derivatives of early representation of the basic hereditary core, influenced by familial and cultural patterns.
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A mailed questionnaire dealing with similarity in childhood, and how often and by whom the twins were mixed up, was applied to 290 same-sex adult twin pairs. For about 75% of pairs ten genetic markers were analysed. The agreement in zygosity classification between questionnaire and blood typing was high. Irrespective of whether raw scores of discriminant function analysis was applied, the agreement was nearly 95%. When a decision tree was applied, the percentage rose to nearly 96%. Considering that probably four of the twin pairs were wrongly classified as MZ by genetic markers, the percentage rose to 96 and 98, respectively.
By means of a twin study an attempt was made to throw light upon the aetiology and nosology of phobic fears. Factor analyses revealed five factors, namely separation fears, animal fears, mutilation fears, social fears and nature fears. The study demonstrated that, apart from separation fears, genetic factors play a part in the strength as well as content of phobic fears. Environmental factors, affecting the development of dependence, reserve and neurotic traits generally, seemed also to be of some importance. It was further demonstrated that phobic fears were related to emotional and social adjustment and this was true to an even greater extent for separation fears.
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Fifty-four patients with schizotypal and/or borderline personality disorders were compared with 165 patients with other personality disorders and 52 patients with no personality disorders as to their perception of parental behavior in childhood. Both schizotypals and borderlines reported low care; however, schizotypals remembered underprotection and borderline overprotection. The study suggests parental neglect in the childhood memory of schizotypals and negative over-involvement for borderlines.
The aim of this study was to investigate the genetic and environmental contribution to common phobic fears, and to relate the findings to contemporary theories about the etiology of common phobic fears. Self-reported common phobic fear was studied in a treatment sample of 23 monozygotic and 38 same-sex dizygotic twin pairs. Heritability of .47 was observed for common phobic fear of small animals and social fear, and a heritability of .30 in common agoraphobic fear. For common fear of nature phenomena and situational fear, the heritability was 0. The finding that common nature and situational fears were solely caused by environmental factors is in support of learning theory, whereas results for animal, social, and other common phobic fear are in support of an integrative theory of biological preparedness, learning history, and a cognitive style of fearful expectation.
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No twin study has previously investigated the whole range of personality disorders (PDs) recorded by interviews. Based on twin and patient registries, 92 monozygotic (MZ) and 129 dizygotic (DZ) twin pairs were interviewed with the Structured Clinical Interview for DSM-III-R Personality Disorders (SCID-II). Observed prevalence rates from a normal population study of more than 2,000 individuals were used in combination with data from the present study to generate statistics assumed to be valid for a normal twin population, and these statistics were used for structural equation modeling. The best-fitting models had a heritability of .60 for PDs generally, .37 for the eccentric (A) cluster, .60 for the emotional (B) cluster, and .62 for the fearful (C) cluster. Among the specific PDs, the heritability appeared to be .79 for narcissistic, .78 for obsessive-compulsive, .69 for borderline, .67 for histrionic, .61 for schizotypal, .57 for dependent, .54 for self-defeating, .29 for schizoid, .28 for paranoid, and .28 for avoidant PDs. The best-fitting models never included shared-in-families environmental effects. However, a model with only shared familial and unique environmental effects could not be ruled out for dependent PD. Shared familial environmental effects may also influence the development of any PD and borderline PD. Passive-aggressive PD did not seem to be affected by genes or family environment at all. The low occurrence of antisocial PD in the twin sample precluded any model for this disorder. PDs seem to be more strongly influenced by genetic effects than almost any axis I disorder, and more than most broad personality dimensions. However, we observed a large variation in heritability among the different PDs, probably partly because of a moderate sample size and low prevalence of the specific disorders.