Schizophrenia and bipolar disorder share genetic root

LONDON (Reuters) - Schizophrenia and bipolar disorder share common genetic causes, according to research published on Friday that suggests the two conditions may simply be different manifestations of the same disease.

Some drugs, such as AstraZeneca's Seroquel and Eli Lilly's Zyprexa, are already used to treat both and the question of whether they represent a disease continuum is widely debated in psychiatry.

Now Swedish researchers have shown that there are strong and inter-related inherited links between both conditions.

An analysis of 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, while evidence from half-siblings suggested the effect was mainly due 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.

"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."

Michael Owen and Nick Craddick of Britain's University of Cardiff said the findings underscored the need to reappraise psychopathology.

"How many distinct disorders it might be useful to recognise, or whether the functional psychoses are better conceptualised as a continuum or as a set of overlapping pathological processes, is not yet known," they wrote in a commentary.

(Reporting by Ben Hirschler; Editing by Erica Billingham)