A twin study of alexithymia.
BACKGROUND
Factors contributing to the development of alexithymia and the nature of alexithymia's relation with trait negative and positive affectivity are unclear. In this study, a twin approach was used to examine the degree of genetic and environmental contributions to the different facets of alexithymia, and the nature of their relations to trait negative and positive affectivity.


METHODS
Forty-five monozygotic and 32 same-sex dizygotic twin pairs completed the Toronto Alexithymia Scale-20, the Eysenck Personality Inventory, and a zygosity questionnaire.


RESULTS
Model fitting analyses indicated that familial influences contributed significantly to all three facets of alexithymia. Parameter estimates and intraclass correlations suggested, though could not confirm, that it was shared environmental factors that contributed to difficulty identifying and communicating emotions (ID and COM), but shared genetic factors that contributed to externally oriented thinking (EOT). Between-twin cross-trait twin analyses revealed strong correlations between ID and neuroticism, and between COM and extraversion, and suggested that it is shared familial influences which account for these associations.


CONCLUSIONS
The results of this study indicate that: (a) the different facets of alexithymia are influenced by familial factors; (b) the previously noted associations between ID and COM and trait affectivity are not merely methodological artifacts; and (c) the associations between ID and COM and trait affectivity are influenced by familial factors. The results also suggest that ID and COM are largely influenced by shared environmental factors, but that EOT is influenced by genetic factors.
Valera
E M
EM
Department of Psychiatry, Massachusetts Mental Health Center, Boston, MA 02115, USA. eve_valera@hms.harvard.edu
Berenbaum
H
H
D000293:Adolescent; D000328:Adult; D000342:Affective Symptoms / Q000523:psychology*; D000704:Analysis of Variance; D004200:Diseases in Twins; D005120:Extraversion, Psychological; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009497:Neurotic Disorders / Q000523:psychology; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires