A common genetic basis has been found for schizophrenia, major depression, attention deficit hyperactivity disorder (ADHD) and bipolar disorder, a new study has found.
A high degree of genetic correlation was found between the four psychiatric conditions in the study, which analysed genomic data from more than one million people.
'One of the big messages is that psychiatric disorders turned out to be very connected on the genetic level,' said study author Dr Verneri Antilla, from the Broad Institute of MIT and Harvard University.
The study, published in Science this week, assessed the genetic information from 265,218 patients with psychiatric and neurological disorders and 784,643 unaffected individuals, looking for links between genetic variants and participants' diagnoses. The authors found that almost all psychiatric disorders assessed, typically thought of as distinct categories for the purposes of diagnosis, actually have considerable genetic overlap.
Several distinct groups of disorders with genetic links emerged in the study. The highest degree of correlation was between schizophrenia, depression, ADHD and bipolar disorder. At the same time, there was significant overlap between anorexia nervosa, obsessive-compulsive disorder (OCD) and schizophrenia. In addition, the study found that depression and Tourette's syndrome had genetic links, as did autism spectrum disorder and schizophrenia.
In contrast, neurological disorders such as Parkinson's and Alzheimer's disease had very little overlap with each other or with the psychiatric disorders studied, suggesting unrelated underlying causes. 'They really do seem distinct, which probably means that the mechanisms of cell death are different,' said Professor John Hardy, chair of molecular biology of neurological disease at University College London, who was not involved in the study.
Interestingly, the authors also found that there was significant genetic overlap between certain disorders and early life measures of cognitive ability, such as years of education and academic attainment. Higher cognitive ability was linked to several disorders including anorexia and bipolar disorder. However, it was negatively correlated with some neurological disorders, for example, Alzheimer's disease and ischaemic stroke.
'This work is starting to reshape how we think about disorders of the brain,' said Dr Ben Neale, also of the Broad Institute and a leader of the project. 'If we can uncover the genetic influences and patterns of overlap between different disorders, then we might be able to better understand the root causes of these conditions – and potentially identify specific mechanisms appropriate for tailored treatments.'