The largest ever genetic study of psychiatric illness has revealed new evidence of overlapping genetic risk factors for major psychiatric conditions.
Psychiatric disorders show a relatively high degree of heritability compared with other complex conditions, and are therefore presumed to involve substantial genetic components. However, the biological causes of most such diseases remain poorly understood, and genomic research can provide valuable insights.
Published in Nature Genetics, the new study is the work of theCross-Disorder Group of the Psychiatric Genomics Consortium (PGC), an international collaboration. Researchers used genome-wide genotype data from cases and controls in schizophrenia, bipolar disorder, major depressive disorder, autism spectrum disorders (ASD) and attention-deficit / hyperactivity disorder (ADHD). They analysed this data using statistical methods to examine genetic variation within and between different diseases.
Broadly, strong genetic links were identified between schizophrenia and bipolar disorder; moderate genetic links between schizophrenia and major depressive disorder, bipolar disorder and major depressive disorder, and ADHD and major depressive disorder; and weak (but still significant) genetic links between schizophrenia and ASD.
It is hoped that these findings, if replicated, will help unravel the biology of the various disorders and the development of better diagnostics and treatments. The researchers also hope to move on to examine the genomics of other conditions such as eating and drug use disorders.
Comment: Diagnosis of specific major psychiatric disorders still relies on the observation of patterns of overlapping symptoms, and there is considerable debate over the spectrum of symptoms and where the boundaries actually lie between one defined disease and another. Genomic data is clearly highly relevant; in the future it may be possible to use it to specify much more precisely which disease or sub-group is present in a patient, much as cancer is rapidly evolving from broad morphology-based diagnoses into molecular sub-classification. The benefit is in allowing more individually tailored clinical management; a form, in effect, of personalised medicine.
However, moves towards genetic elements for diagnosis of psychiatric conditions may inevitably raise concerns about predictive genetic testing. Whilst (as for cancer) the individual variability in contributing genetic and environmental factors is unlikely to allow useful predictive testing in most cases – the authors themselves note that even the strongest genetic links confer only a moderately elevated disease risk for family members - it will be important to address worries about the impact of any new genetic disease classification as the science moves forward.