Largest twin study pins nearly 80% of schizophrenia risk on heritability

A new study in Biological Psychiatry looks at the risk for schizophrenia in twins

In the largest study of twins in schizophrenia research to date, researchers at the University of Copenhagen, Denmark, estimate that as much as 79% of schizophrenia risk may be explained by genetic factors. The estimate indicates that genetics have a substantial influence on risk for the disorder.

Published in Biological Psychiatry, the study used a new statistical approach to address one of the factors that contributes to inconsistencies across previous studies—usually studies of heritability require that people be classified as either having schizophrenia or not, but some people at risk could still develop the disease after the study ends. Drs. Hilker, Helenius and colleagues applied a new method to take this problem into account, making the current estimates likely the most accurate to date.

“The new estimate of heritability of schizophrenia, 79%, is very close to the high end of prior estimates of its heritability,” said Dr. John Krystal, Editor of Biological Psychiatry, referring to previous estimates that have varied between 50% and 80%. “It supports the intensive efforts in place to try to identify the genes contributing to the risk for developing schizophrenia,” said Dr. Krystal, which have been built on the idea that schizophrenia is highly heritable based on the findings of generations of twin studies.

The study took advantage of the nationwide Danish Twin Register—a record of all twins born in Denmark since 1870—coupled with information from the Danish Psychiatric Central Research Register, to assess genetic liability in over 30,000 pairs of twins.

Because the diagnosis of schizophrenia is based on a narrow definition of symptoms, the researchers also estimated heritability using a broader illness category including related disorders on the schizophrenia spectrum. They found a similar estimate of 73%, indicating the importance of genetic factors across the full illness spectrum.

Dr. Hilker explained, “This study is now the most comprehensive and thorough estimate of the heritability of schizophrenia and its diagnostic diversity. It is interesting since it indicates that the genetic risk for disease seems to be of almost equal importance across the spectrum of schizophrenia,” even though the clinical presentation may range from severe symptoms with lifelong disability to more subtle and transient symptoms. “Hence, genetic risk seems not restricted to a narrow illness definition, but instead includes a broader diagnostic profile,” she added.

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Notes for editors
The article is "Heritability of schizophrenia and schizophrenia spectrum based on the nationwide Danish Twin Register," by Rikke Hilker, Dorte Helenius Mikkelsen, Birgitte Fagerlund, Kaare Christensen, Axel Skytthe, Thomas Werge, Merete Nordentoft, and Birte Glenthøj (http://dx.doi.org/10.1016/j.biopsych.2017.08.017). It appears in Biological Psychiatry, published by Elsevier.

Copies of this paper are available to credentialed journalists upon request; please contact Rhiannon Bugno at Biol.Psych@UTSouthwestern.edu or +1 214 648 0880. Journalists wishing to interview the authors may contact Rikke Hilker, MD, PhD at rikke.hilker@regionh.dk.

The authors’ affiliations and disclosures of financial and conflicts of interests are available in the article.

John H. Krystal, M.D., is Chairman of the Department of Psychiatry at the Yale University School of Medicine, Chief of Psychiatry at Yale-New Haven Hospital, and a research psychiatrist at the VA Connecticut Healthcare System. His disclosures of financial and conflicts of interests are available here.

About Biological Psychiatry
Biological Psychiatry is the official journal of the Society of Biological Psychiatry, whose purpose is to promote excellence in scientific research and education in fields that investigate the nature, causes, mechanisms and treatments of disorders of thought, emotion, or behavior. In accord with this mission, this peer-reviewed, rapid-publication, international journal publishes both basic and clinical contributions from all disciplines and research areas relevant to the pathophysiology and treatment of major psychiatric disorders.

The journal publishes novel results of original research which represent an important new lead or significant impact on the field, particularly those addressing genetic and environmental risk factors, neural circuitry and neurochemistry, and important new therapeutic approaches. Reviews and commentaries that focus on topics of current research and interest are also encouraged.

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Rhiannon Bugno
Editorial Office, Biological Psychiatry
+1 214 648 0880
Biol.Psych@UTSouthwestern.edu