The estimated 79% heritability of schizophrenia is congruent with previous reports and indicates a substantial genetic risk

Heritability of schizophrenia and schizophrenia spectrum based on the nationwide Danish Twin Register. Rikke Hilker, MD, PhD. Biological Psychiatry. https://doi.org/10.1016/j.biopsych.2017.08.017

Abstract

Background: Twin studies have provided evidence that both genetic and environmental factors contribute to schizophrenia risk. Heritability estimates of schizophrenia in twin samples have varied methodologically. This study provides updated heritability estimates based on nationwide twin data and an improved statistical methodology.

Method: Combining two nationwide registers, the Danish Twin Register and the Danish Psychiatric Research Register, we identified a sample of twins born 1951-2000 (N=31,524 twin pairs). Twins were followed up until June 1st 2011. Liability threshold models adjusting for censoring with inverse probability weighting were used to estimate probandwise concordance rates and heritability of the diagnoses of schizophrenia and schizophrenia spectrum disorders.

Results: The probandwise concordance rate of schizophrenia is 33% in monozygotic (MZ) twins and 7% in dizygotic (DZ) twins. We estimated the heritability of schizophrenia to be 79%. When expanding illness outcome to include schizophrenia spectrum disorders, the heritability estimate was almost similar, 73%.

Conclusion: 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 schizophrenia is congruent with previous reports and indicates a substantial genetic risk. The high genetic risk also applies to a broader phenotype of schizophrenia spectrum disorders. The low concordance rate of 33% in MZ twins demonstrates that illness vulnerability is not solely indicated by genetic factors.

Key words: Heritability schizophrenia twin study censoring concordance register