Psychiatric disorders such as schizophrenia and bipolar disorder often run in families. In a new international collaboration, researchers explored the genetic connections between these and other disorders of the brain at a scale that far eclipses previous work on the subject. The team determined that psychiatric disorders share many genetic variants, while neurological disorders appear more distinct.

The study takes the broadest look yet at how genetic variation relates to brain disorders. The results indicate that psychiatric disorders likely have important similarities at a molecular level, which current diagnostic categories do not reflect.

Disorders Of Brain

This work is starting to re-shape how we think about disorders of the brain. If they can uncover the genetic influences and patterns of overlap between different disorders, then we might be able to understand the causes of these conditions better and potentially identify specific mechanisms appropriate for tailored treatments.

Psychiatric Diseases

To examine the biological overlap between these disorders, researchers must rely on genetics. For the current study, international consortia pooled their data to examine the genetic patterns across 25 psychiatric and neurological diseases. 

Because each genetic variant only contributes a tiny percentage of the risk for developing a given disorder, the analyses required huge sample sizes to separate reliable signals from noise. The final results indicated widespread genetic overlap across different types of psychiatric disorders, particularly between attention-deficit/hyperactivity disorder (ADHD), bipolar disorder, major depressive disorder, and schizophrenia. 

Additionally, within the cognitive measures, the researchers were surprised to note that genetic factors predisposing individuals to certain psychiatric disorders namely anorexia, autism, bipolar, and OCD were significantly correlated with factors associated with higher childhood cognitive measures, including more years of education and college attainment. 

Neurological disorders, however, particularly Alzheimer's and stroke, were negatively correlated with those same cognitive measures. They were surprised that genetic factors of some neurological diseases, normally associated with the elderly, were negatively linked to genetic factors affecting early cognitive measures. It was also surprising that the genetic factors related to many psychiatric disorders were positively correlated with educational attainment.

Heritability

The high degree of genetic correlation among many of the psychiatric disorders adds further evidence that their current clinical boundaries do not reflect distinct underlying pathogenic processes, at least on the genetic level.  This suggests a deeply interconnected nature for psychiatric disorders, in contrast to neurological disorders, and underscores the need to refine psychiatric diagnostics.

Genetically informed analyses may provide important “scaffolding” to support such restructuring of psychiatric nosology, which likely requires incorporating many levels of information. They show that both psychiatric and neurological disorders have robust correlations with cognitive and personality measures.

Further study is needed to evaluate whether overlapping genetic contributions to psychiatric pathology may influence treatment choices. Ultimately, such developments may pave the way toward reduced heterogeneity and improved diagnosis and treatment of psychiatric disorders.