Abstract
Background
Twin studies have provided evidence that both genetic and environmental factors contribute
to schizophrenia (SZ) risk. Heritability estimates of SZ in twin samples have varied
methodologically. This study provides updated heritability estimates based on nationwide
twin data and an improved statistical methodology.
Methods
Combining two nationwide registers, the Danish Twin Register and the Danish Psychiatric
Research Register, we identified a sample of twins born between 1951 and 2000 (N = 31,524 twin pairs). Twins were followed until June 1, 2011. Liability threshold
models adjusting for censoring with inverse probability weighting were used to estimate
probandwise concordance rates and heritability of the diagnoses of SZ and SZ spectrum
disorders.
Results
The probandwise concordance rate of SZ is 33% in monozygotic twins and 7% in dizygotic
twins. We estimated the heritability of SZ to be 79%. When expanding illness outcome
to include SZ spectrum disorders, the heritability estimate was almost similar (73%).
Conclusions
The key strength of this study is the application of a novel statistical method accounting
for censoring in the follow-up period to a nationwide twin sample. The estimated 79%
heritability of SZ is congruent with previous reports and indicates a substantial
genetic risk. The high genetic risk also applies to a broader phenotype of SZ spectrum
disorders. The low concordance rate of 33% in monozygotic twins demonstrates that
illness vulnerability is not solely indicated by genetic factors.
Keywords
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Article info
Publication history
Published online: August 30, 2017
Accepted:
August 22,
2017
Received in revised form:
August 22,
2017
Received:
January 18,
2017
Identification
Copyright
© 2017 Society of Biological Psychiatry.
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