A new study on the link between bipolar disorder and schizophrenia has found evidence that the two disorders share common genetic causes. The study offers an answer to the debate that has stirred the interest of scientists for more than a decade.

 

A number of studies focusing on the genetic causes of schizophrenia have found that, acting in some combinations, genetic variations may have a major influence on someone’s mental state. The disorder affects 1 percent of the population and causes scrambled thinking and delusions. Experts detected rare and unknown mutations that turned up three to four times as often in people with schizophrenia compared to those without it.

 

But earlier studies in families have not supported the idea that schizophrenia and bipolar disorder may share a common genetic cause.

Now Swedish researchers have managed to show that there are strong inherited similarities between both conditions. The study, which included 9 million Swedish people over a 30-year period, found close relatives of people with schizophrenia or bipolar disorder had an increased risk of both disorders. Of the participants, 35,985 people were diagnosed with schizophrenia and 40,487 people with bipolar disorder. An analysis of data from half-siblings suggested the effect was mainly attributable to genetic factors.

 

“We showed evidence that schizophrenia and bipolar disorder partly share a common genetic cause,” Paul Lichtenstein and colleagues at Stockholm's Karolinska Institute reported in The Lancet medical journal.

According to the study, first-degree relatives of people with either schizophrenia or bipolar disorder were at increased risk for both of the psychiatric disorders. Siblings of schizophrenics were nine times more likely than the general population to have schizophrenia and four times more likely to have bipolar disorder. 

Those with bipolar siblings were 7.9 times more likely to be bipolar and 3.9 more likely to be schizophrenic.

 

Schizophrenia symptoms include distorted thoughts and hallucinations (perception in the absence of a stimulus). It most commonly manifests as auditory halucinatons, paranoid or bizarre delusions, or disorganized speech and thinking with significant social or occupational dysfunction. The disorder primarily affects cognition, but it may contribute to chronic problems with behaviour and emotion.

 

Bipolar disorder describes a category of mood disorders which may include episodes of abnormally elevated mood called mania or hypomania. Patients may experience depressive episodes or symptoms, or mixed episodes in which features of both mania and depression are present at the same time. Bipolar disorder also carries a high risk of suicide. It’s still unclear what causes the disease but genetic factors are definitely playing a major role, as the disease was found to run in families. Other than a family history of psychotic disorders, few risk factors for the condition have been identified. People diagnosed with bipolar disorder receive medication such as mood stabilizers, anti-psychotic and antidepressants.

In the U.S., 5.7 million adults suffer from the disorder, according to the US National Institute of Mental Health. About 1 in 100 people develop bipolar disorder in their life time.