Five mental disorders linked by genetic traits
Five major mental disorders may be linked to the same common inherited genetic variations, according to a study published in the journal Nature Genetics.
Researchers from the Cross Disorders Group of the Psychiatric Genomic Consortium (PGC) made the discovery, using genome-wide genotype data in a study of people with five mental disorders. They also had controls to account for various factors during the analysis.
The five mental disorders they monitored were as follows:
2. Bipolar disorder;
3. Major depressive disorder;
4. Autism spectrum disorders; and
5. Attention-deficit hyperactivity disorder (ADHD).
In a prior study, the researchers previously reported the first link between these psychiatric conditions, showing that those with the five conditions had a greater probability of having variation within the same four chromosomal sites.
This most recent study, however, has investigated the links in more detail by using the same genome-wide information and large data sets.
Thousands of people with each of the five disorders were involved in the study that analyzed their genetic variation, which researchers compared with the genetic codes of those without the disorders. They then calculated the extent to which pairs of disorders were linked to the same genetic variants.
The findings of the analysis revealed the following connections that can be attributed to inherited genetic factors between certain mental disorders as a result of common genetic variation:
• Schizophrenia and bipolar disorder - 15%
• Bipolar disorder and depression - 10%
• Schizophrenia and depression - 9%
• Schizophrenia and autism - 3%.
According to the researchers, common genetic variation accounted for between 17 to 28 percent of the risk of all five psychiatric conditions.
“Since our study only looked at common gene variants, the total genetic overlap between the disorders is likely higher,” said Naomi Wray of the University of Queensland, Australia. “Shared variants with smaller effects, rare variants, mutations, duplications, deletions, and gene-environment interactions also contribute to these illnesses."
The researchers reported that these results, especially the genetic evidence linking schizophrenia and depression, could have important implications for diagnostics and research.
"Such evidence quantifying shared genetic risk factors among traditional psychiatric diagnoses will help us move toward classification that will be more faithful to nature," said Bruce Cuthbert, director of the National Institute of Mental Health.
While the results of the study "attach numbers" to molecular evidence showing the importance of connections that can be attributed to inherited genetic factors linked to common genetic variation, which causes these five psychiatric disorders, the researchers point out that much of the inherited genetic contribution to these disorders is unexplained. Same goes for non-inherited genetic factors.
The authors of the study explain further, using the example of how common genetic variation accounts for 23% of schizophrenia patients, and evidence from twin and family studies estimate schizophrenia's total heritability at 81%.
"It is encouraging that the estimates of genetic contributions to mental disorders trace those from more traditional family and twin studies. The study points to a future of active gene discovery for mental disorders,” said Thomas Lehner, chief of the genomics research branch at the National Institute of Mental Health.
SOURCE: Nature Genetics, “Genetic relationship between five psychiatric disorders estimated from genome-wide SNPs,” published online August 11, 2013 (doi:10.1038/ng.2711).