Five major mental illnesses are genetically linked

Mental disorders, including schizophrenia, bipolar disorder and major depression, have some common genetic variants that account for significant risk of crossover disease, according to research published August 11 in Nature Genetics.

Naomi R. Wray, MD, a researcher from the University of Queensland, Brisbane, Australia, and other colleagues from the Cross Disorders Group of the Psychiatric Genomics Consortium and the National Institute of Mental Health conducted the first-ever multi-center study to find genetic overlap between these and other mental disorders such as attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorders (ASD). Findings showed that shared genetic variation makes up 17 to 29 percent of risk of developing disease.

“Since our study only looked at common gene variants, the total genetic overlap between the disorders is likely higher,” stated Wray in an NIH press release. “Shared variants with smaller effects, rare variants, mutations, duplications, deletions, and gene-environment interactions also contribute to these illnesses.”

It is well established that a majority of psychiatric disorders involve at least some if not high risk of genetic heritability, but researchers have not been able to point to which variants are involved solely in one disorder and which range between multiple disorders. Scientists scoped the etiology of genetic mental disorder by performing a complete search of genotypes available from the Psychiatric Genomics Consortium and conducting both univariate and bivariate analysis to estimate variation both inherent in these and spanning other psychiatric disorders.

The study showed that not only do single nucleotide polymorphisms account for up to 29 percent of variance in patient risk, but strong correlations were found between major disorders. The calculated correlation between schizophrenia and major bipolar disorder was approximately 0.68, and between bipolar disorder and major depression it was 0.47. Major depressive disorder was also linked to schizophrenia, with a calculated correlation of 0.43, as well as with ADHD, with a correlation estimated at 0.32. There was significantly less co-heritability between schizophrenia and ASD, pegged at a correlation of approximately 0.16, and no significant correlation was found between other matched disorders or between these and a control group related to Crohn’s disease.

“This empirical evidence of shared genetic etiology for psychiatric disorders can inform nosology and encourages the investigation of common pathophysiologies for related disorders,” wrote the authors.