In two separate studies, international researchers have exposed genetic variations associated with schizophrenia and bipolar disorder, and also showed evidence for shared genetic links between the diseases.
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PARIS: Broad sweeps of the human genome have exposed genetic mutations that heighten the risk of schizophrenia and bipolar disorder, according to two international studies.
The independent studies, each conducted by a consortium of about 200 scientists and published in Nature Genetics, also found significant genetic overlap between the debilitating mental disorders.
The first study identified five genomic variants newly associated with schizophrenia - a disease where patients typically hear voices that are not real, tend toward paranoia and suffer from disorganized speech and thinking.
"The reason why there have been five novel regions identified is because this study screened the DNA of over 50,000 individuals," said psychiatrist and co-author Bryan Mowry from the University of Queensland in Brisbane.
"We can now more intensely investigate each of these regions to look for and try to identify causal variants," he said.
Bipolar disorder
The other study, led by neuroscientist Pamela Sklar from the Mount Sinai School of Medicine in New York, confirmed a significant link with a gene, CACNA1C, that has been previously associated with schizophrenia.
It also uncovered a new gene variant at another location, known as ODZ4, which suggests neurochemical channels in the brain activated by calcium play a role in boosting the risk of developing the disease.
Previously known as manic depression, bipolar disorder is characterised by hard-to-control mood swings that veer back-and-forth between depression and euphoria, and afflicts a slightly smaller percentage of the population.
The biological profile of both conditions remains almost entirely unknown.
Complex heritable relationship
Scientists have long observed that each syndrome tends to run in families, suggesting a powerful inherited component.
But early hopes of finding a single-gene culprit swiftly faded, giving way to the realisation that - to the extent DNA is at fault - blame is probably spread across dozens, maybe even hundreds of DNA variants.
Genome-wide comparisons made possible by gains in computing power involve sweeps of tens of thousands of individual genetic codes from patients and otherwise healthy counterparts.
But so far only a handful of suspects have been found that, at best, account for about 30 percent of the heritable component of schizophrenia.
Nailing down genetic drivers is made even harder by uncertainty as to whether schizophrenia and bipolar - defined by a varying constellation of symptoms - are single or multiple diseases.
Mass study yields clues
In one of the largest gene sweeps so far, Pablo Gejman of the University of Chicago and colleagues worldwide started by reviewing 17 earlier efforts involving nearly 22,000 people, just under half of them schizophrenia patients.
