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.
Bibliographical noteFunding Information:
This work was supported by Sygekassernes Helsefond, Forskerakademiet, Forskningsinitiativet under Århus University; the Theodore and Vada Stanley Foundation, Fonden til Forskning af Sindslidelse, Fonden til Psykiatriens Fremme (Petra & Cris Andersens Fond) and Eli Lilly Denmark AIS; and a Vassar College study leave to SLT. IIG was supported by the Lieber Prize for Schizophrenia Research and the University of Louisville Grawemeyer Award in Psychology.
© 2015, Springer Science+Business Media New York.
- Affective psychoses