July 12, 2018
According to a new study published in Science,1 psychiatric disorders — unlike genetically distinct neurological disorders — may share important similarities at a molecular level. In this international collaboration, researchers found widespread genetic overlap across different types of psychiatric disorders, most notably attention deficit hyperactivity disorder (ADHD or ADD), anxiety disorders, bipolar disorder, major depressive disorder (MDD), and schizophrenia.
To perform a comprehensive heritability and correlation analysis of genetic patterns across 25 brain disorders, researchers included any meta-analyses of any common brain disorders for which they were able to identify a genome-wide association study (GWAS) with sufficient sample size. The total study sample comprised 265,218 patients with different brain disorders and 784,643 healthy individuals who served as the control group. The researchers also examined the relationship between brain disorders and 17 physical or cognitive measures, such as years of education, from almost 1.2 million people.
Results showed that ADHD, anxiety disorders, bipolar disorder, MDD, and schizophrenia shared a high degree of reciprocal correlation [average genetic correlation (rg) = 0.40]. Researchers also noted a strong correlation between anorexia nervosa, obsessive-compulsive disorder (OCD), and schizophrenia, as well as between Tourette syndrome, OCD, and MDD.
In contrast, neurological disorders appeared more distinct from one another compared with psychiatric disorders, suggesting greater diagnostic specificity and/or more distinct origins. Parkinson disease, Alzheimer disease, generalized epilepsy, and multiple sclerosis showed little to no correlation with other brain disorders.
The only significant cross-category correlations were between migraine and ADHD, MDD, and Tourette syndrome.
More years of education and college attainment were positively correlated with certain psychiatric disorders – namely anorexia nervosa, autism spectrum disorder, bipolar disorder, OCD, and schizophrenia. However, neurological disorders like Alzheimer and stroke were negatively correlated with those same cognitive measures.
“It was… surprising that the genetic factors related to many psychiatric disorders were positively correlated with educational attainment,” said co-author Verneri Anttila, a research fellow at the Broad Institute of Cambridge, in a press release.2 “We’ll need more work and even larger sample sizes to understand these connections.”
Consistent with a previous meta-analysis,3 body mass index showed significant positive genetic correlation to ADHD.
As noted in the study’s press release, “the high degree of genetic correlation among the psychiatric disorders suggests that current clinical categories do not accurately reflect the underlying biology.” “This study may provide important ‘scaffolding’ to support a framework for investigating mental disorders, incorporating many levels of information to understand basic dimensions of brain function,” concluded the authors.
3Cortese S, Moreira-Maia CR, St Fleur D, Morcillo-Peñalver C, Rohde LA, Faraone SV. “Association Between ADHD and Obesity: A Systematic Review and Meta-Analysis.” The American Journal of Psychiatry. 2016 January;173(1):34-43. doi: 10.1176/appi.ajp.2015.15020266
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