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| |  Study: Bipolar Disorder, Schizophrenia Share Common Genetic Causes NEW YORK -- January 15, 2009 -- An analysis of 9 million Swedish people from a 30-year period has shown that bipolar disorder and schizophrenia share common genetic causes. The findings are published in the January 17 issue of The Lancet. Whether these 2 conditions are the clinical outcomes of distinct or shared processes is much debated in psychiatry. Paul Lichtenstein, MD, and Christina Hultman, MD, Karolinska Institutet, Stockholm, Sweden, and colleagues aimed to solve this dilemma using data from Sweden's multi-generation register, featuring some 9 million individuals from 2 million families in the period from 1973 to 2004. Risks for schizophrenia, bipolar disorder, and their occurrence with each other were assessed for biological and adoptive parents, offspring, full siblings, and half-siblings of people with 1 of the diseases. First-degree relatives of people with either schizophrenia (n=35,985) or bipolar disorder (n=40,487) were at increased risk of these conditions. Full siblings were 9 times more likely than the general population to have schizophrenia and 8 times more likely to have bipolar disorder. Maternal half-siblings were 3.6 times more likely to have schizophrenia and 4.5 more times more likely to have bipolar disorder than the general population; the risk was lower for paternal half-siblings, who were 2.7 times more likely to have schizophrenia and 2.4 times more likely to have bipolar disorder. When relatives of people with bipolar disorder were analysed, increased risks for schizophrenia also existed for all relationships, including adopted children to their biological parents with bipolar disorder. Heritability was found to be 64% for schizophrenia and 59% for bipolar disorder. The causes for the comorbidity between the 2 conditions were to a large extent (63%) due to genetic factors. "Similar to molecular genetic studies, we showed evidence that schizophrenia and bipolar disorder partly share a common genetic cause," the authors wrote. "These results challenge the current nosological dichotomy between schizophrenia and bipolar disorder, and are consistent with a reappraisal of these disorders as distinct diagnostic entities." "Within clinical practice, the underlying structure of psychosis and the knowledge of the common causes of these disorders might be beneficial for treatment options and development of psychosis medication," they concluded. SOURCE: The Lancet
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