A broad-based study of data from more than two million nuclear families in Sweden has provided evidence of possible common genetic determinants of schizophrenia and bipolar disorder.
Reporting their results in the January 17 issue of the journal The Lancet, the authors, who include NARSAD Distinguished Investigator Tyrone D. Cannon, Ph.D., of UCLA, explained the goal of their study.
"Whether schizophrenia and bipolar disorder are the clinical outcomes of discrete or shared causative processes is much debated in psychiatry. We aimed to assess genetic and environmental contributions to liability for schizophrenia, bipolar disorder, and their comorbidity."
To achieve their goal, the researchers merged data from the Swedish multigeneration population register, which contains information about all children and their parents in Sweden, and the hospital discharge register, which includes all public psychiatric inpatient admissions in Sweden and the Swedish hospital discharge register. These data spanned the period 1973 to 2004.
Risks for schizophrenia, bipolar disorder and their comorbidity were assessed for biological and adoptive parents, offspring, and full and half-siblings of individuals with one of the diseases. The results, the researchers stated, clearly showed increased risks of both schizophrenia and bipolar disorder for first-degree relatives with either disorder. Evidence from half-siblings and offspring adopted away shows that this is due substantially to genetic factors.
"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 dichotomy between schizophrenia and bipolar disorder, and are consistent with a reappraisal of these disorders as distinct diagnostic entities."
An editorial note accompanying the article asserts the significance of the breadth of the study, as opposed to most previous genetic epidemiological studies, which �have been underpowered to investigate the question of diagnostic overlap.�