RESUMEN
We studied schizophrenia liability in a Danish population-based sample of 44 twin pairs (13 MZ, 31 DZ, SS plus OS) in order to replicate previous twin study findings using contemporary diagnostic criteria, to examine genetic liability shared between schizophrenia and other disorders, and to explore whether variance in schizophrenia liability attributable to environmental factors may have decreased with successive cohorts exposed to improvements in public health. ICD-10 diagnoses were determined by clinical interview. Although the best-fitting, most parsimonious biometric model of schizophrenia liability specified variance attributable to additive genetic and non-shared environmental factors, this model did not differ significantly from a model that also included non-additive genetic factors, consistent with recent interview-based twin studies. Schizophrenia showed strong genetic links to other psychotic disorders but much less so for the broader category of psychiatric disorders in general. We also observed a marginally significant decline in schizophrenia variance attributable to environmental factors over successive Western European cohorts, consistent perhaps with improvements in diagnosis and in prenatal and perinatal care and with a secular decline in the prevalence of schizophrenia in that region.
Asunto(s)
Trastornos Psicóticos Afectivos/genética , Predisposición Genética a la Enfermedad , Entrevistas como Asunto , Esquizofrenia/genética , Gemelos/genética , Adulto , Estudios de Cohortes , Intervalos de Confianza , Femenino , Humanos , Masculino , Gemelos Dicigóticos/genética , Gemelos Monocigóticos/genética , Adulto JovenRESUMEN
BACKGROUND: A previous study demonstrated a 40% higher rate of schizophrenia in dizygotic twins than in the general population. The aim of the present study is to evaluate whether genes influencing the rate of dizygotic twinning and genes of importance for developing schizophrenia can be associated. METHOD: Through record linkage between The Danish Twin Register, The Danish Psychiatric Central Register, and The Danish Civil Registration System, the rate of schizophrenia in singleton siblings of dizygotic and monozygotic twins was compared with the rate in siblings of singletons. RESULTS: The rate of first admission to hospital for schizophrenia in siblings of dizygotic twins was 35% greater than the rate in siblings of singletons. The result was statistically significant (p = 0.04). The rate in siblings of monozygotic twins was not increased. CONCLUSION: The results are in accordance with a theory of a linkage between genes influencing the rate of dizygotic twinning and genes influencing the threshold for developing schizophrenia.
Asunto(s)
Enfermedades en Gemelos/genética , Esquizofrenia/genética , Gemelos Dicigóticos/genética , Estudios Transversales , Dinamarca/epidemiología , Femenino , Predisposición Genética a la Enfermedad/genética , Humanos , Masculino , Sistema de Registros , Factores de Riesgo , Esquizofrenia/epidemiología , Gemelos Monocigóticos/genéticaRESUMEN
BACKGROUND: A previous study demonstrated a higher rate of schizophrenia in dizygotic twins than in the general population, and a higher rate of schizophrenia in siblings of dizygotic twins than in siblings of monozygotic twins and singletons, pointing to a common genetic predisposition for dizygotic twinning and schizophrenia. The aim of the present study was to investigate whether these findings also apply to bipolar disorder. METHODS: Through record linkage between The Danish Twin Register, The Danish Psychiatric Central Register and The Danish Civil Registration System, the rate of bipolar disorder (diagnosed for the first time during admission to hospital) in dizygotic and monozygotic twins was compared with the rate in singletons, and the rate in siblings and parents of twins was compared with the rate in siblings and parents of singletons. RESULTS: The rate of bipolar disorder was the same in dizygotic twins, monozygotic twins and singletons as well as for parents and siblings of dizygotic twins, monozygotic twins and singletons. LIMITATIONS: The study is a register-based study, only including hospitalized patients. CONCLUSION: This study shows that there is an equal rate of bipolar disorder in twins and in singletons. Assuming that DZ twinning is under some genetic influence, a differential relationship between schizophrenia and DZ twinning on one hand and bipolar disorder and DZ twinning on the other hand may suggest differences in the genetic basis of the two diseases. The finding that the rate of bipolar disorder in monozygotic twins is the same as the rate of bipolar disorder in singletons supports studies finding no association between bipolar disorder and obstetric complications.