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Increased Occurrence of Schizophrenia and other Psychiatric Illnesses Among Twins

  • Ulla Kläning (a1), Preben Bo Mortensen (a1) and Kirsten Ohm Kyvik (a2)



We wished to establish whether the occurrence of schizophrenia among twins is the same as among the general population.


Through record linkage between the New Danish Twin Register and the Danish Psychiatric Case Register, the twins who have ever received a diagnosis of schizophrenia were identified. Through indirect standardisation for age, sex and dates of admission, the rate of first admission with diagnosis schizophrenia among twins is compared to the same rate in the general population.


A 28% increase in the rate of first admissions for schizophrenia in twins compared to the general population was found. This is statistically significant and does not seem to be caused by any known methodological problems. Twins also had an increased first-admission rate of any psychiatric disorders.


This increased risk does not seem to be explained by known methodological problems, but does differ from earlier studies.


Corresponding author

Ulla Kläning, Institute for Basic Psychiatric Research, Department of Psychiatric Demography, Psychiatric Hospital in Aarhus, DK-8240 Risskov, Denmark


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Allen, M. G. & Pollin, W. (1970) Schizophrenia in twins and the diffuse ego boundary hypothesis. American Journal of Psychiatry, 127, 7984.
Breslow, N. E. & Day, N. E. (1987) Statistical Methods in Cancer Research, Volume II. The Design and Analysis of Cohort Studies. Lyon: IARC, Scientific Publications.
Bryan, E. (1992) Twins and Higher Multiple Births. A Guide to Their Nature and Nurture. London: Edward Arnold.
Chitkara, B., Macdonald, A. & Reveley, A. M. (1988) Twin birth and adult psychiatric disorder. An examination of the case records of the Maudsley Hospital. British Journal of Psychiatry, 152, 391398.
Clayton, D. & Hills, M. (1993) Statistical Models in Epidemiology. Oxford: Oxford University Press.
Dupont, A. (1983) A national psychiatric case register as a tool for mental health planning, research, and administration. The Danish model. In Information Support to Mental Health Programs (eds Laska, E. M., Walter, H., Gulbinat, W. H., et al), pp. 257274. New York: Human Sciences Press.
Eaton, W. W. (1991) Update on the epidemiology of schizophrenia. Epidemiological Reviews, 13, 320328.
Epicenter Software (1989) EPILOG PLUS Statistical Package for Epidemiology and Clinical Trials. Pasadena: Epicenter Software.
Faraone, S. W., Chen, W. I., Goldstein, J. M., et al (1994) Gender differences in age at onset of schizophrenia. British Journal of Psychiatry, 164, 625629.
Fischer, M. (1973) Genetic and environmental factors in schizophrenia. A study of schizophrenic twins and their families. Acta Psychiatrica Scandinavica, suppl. 238.
Goldstein, J. M., Faraone, S. V., Chen, W. J., et al (1990) Sex differences in the familial transmission of schizophrenia. British Journal of Schizophrenia, 156, 819826.
Gottesman, I. I. & Shields, J. (1972) Schizophrenia and Genetics, a Twin Vantage Point. London: Academic Press.
Kringlen, E. (1967) Heredity and Environment in the Functional Psychoses. An Epidemiological Clinical Twin Study. London: William Heinemann Medical.
Kyvik, K. O., Green, A. & Beck-Nielsen, H. (1995) The new Danish twin register Establishment and analysis of twinning rates. International Journal of Epidemiology, 24, 589596.
McNeil, T. F. (1995) Perinatal risk factors and schizophrenia: Selective review and methodological concerns. Epidemiological Reviews, 17, 107112.
Mortensen, P. B. & Eaton, W. W. (1994) Predictors for readmission risk in schizophrenia. Psychological Medicine, 24, 223232.
Munk-Jørgensen, P., Kastrup, M. & Mortensen, P. B. (1993) The Danish psychiatric register as a tool in epidemiology. Acta Psychiatrica Scandinavica, Suppl. 370, 2732.
Pernoll, M. (1991) Current Obstetrics and Gynaecology. Diagnosis and Treatment. London: Prentice Hall.
Rosenthal, D. (1960) Confusion of identity and the frequency of schizophrenia in twins. Archives of Genetic Psychiatry, 3, 297304.
Scott, J. R. (1990) Danforths Obstetrics and Gynaecology. Philadelphia: Lippicott.
Seeman, M. V. (1986) Current outcome in schizophrenia: women vs men. Acta Psychiatrica Scandinavica, 73, 609617.
Tienari, P. (1963) Psychiatric illnesses in identical twins. Acta Psychiatrica Scandinavica, Suppl. 171, 39, 116117.


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Increased Occurrence of Schizophrenia and other Psychiatric Illnesses Among Twins

  • Ulla Kläning (a1), Preben Bo Mortensen (a1) and Kirsten Ohm Kyvik (a2)
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