In analyzing three decades of generational information on 2 million families in Sweden, researchers from the Karolinska Institute in Stockholm found that blood relatives of people with either mental disorder had a notably higher risk of developing bipolar disorder or schizophrenia during their lives, compared to the general population.

According to the study, brothers or sisters of people with these conditions were nine times more likely to be schizophrenic and had eight times the risk of developing bipolar disorder.

The odds were less steep but still high for half-siblings. Brothers and sisters with the same mother had a 3.6 times greater chance of having schizophrenia and a 4.5 times greater risk of bipolar disorder. Paternal half-siblings were roughly 2.5 times more likely to have either condition.

Increased risk of schizophrenia was also found in relatives of people with bipolar disorder. This included adopted children if their biological parents had bipolar disorder.

"Similar to molecular genetic studies, we showed evidence that schizophrenia and bipolar disorder partly share a common genetic cause. These results challenge the current nosological (disease classification) dichotomy between schizophrenia and bipolar disorder, and are consistent with a reappraisal of these disorders as distinct diagnostic entities," the authors wrote.

Schizophrenia and Bipolar Disorder Linked With 'Emptier Brains'

Other research has found that adolescents who experience the first outbreak of psychosis have less grey matter than healthy teenagers. The change was noted in patients suffering from various psychoses, including bipolar illness and schizophrenia, according to the study led by Gregorio Maranon University Hospital, Madrid and Network of Centres for Biomedical Research in Mental Health Networks (CIBERSAM).

The study aimed to examine and locate differences in the volume of grey matter in healthy brains (controls) and those diagnosed with psychotic outbreaks in infancy or adolescence.

The researchers broke such psychosis down into three sub-groups schizophrenia, bipolar disorder and other psychoses that did not fit into either of the other two classifications.

The study analysed a sample of 121 people aged between 7 and 18. All the patients and controls were examined using magnetic resonance imaging in order to detect any possible changes in the structure of their brains.

"The interesting thing was that we found common alterations among those with two types of clinically-differentiated psychoses, schizophrenia and bipolar disorder, and this could help to improve diagnosis of these illnesses," said Santiago Reig, co-author and imaging researcher at the Gregorio Hospital.

The study confirmed these lower levels of grey matter, the brain substance in which neurone cells are concentrated. This lack, which was shared between the schizophrenia and type one bipolar illness sufferers, means the functions of this part of the brain are "somehow atrophied," said Reig. In addition, the technique used by the experts can pinpoint the location of these alterations.

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