[Are variations of structural neuro-anatomy promising endophenotype candidates in bipolar disorder?]

Bipolar disorder is a complex pathology which has a strong heritability component. Epidemiologic studies have pinpointed the contribution of genetic factors to the heritability component. The molecular studies, that have used classical genetic approaches, have been inconclusive at indentifying genes involved in the etiology of this disorder. To overcome these difficulties, a number of strategies have been developed. One of them is the endophenotypic approach. Its main scope is to identify biological markers that are influenced by genetic factors that are less complex than those involved in the clinical expression of the disorder. Thus, it is likely these markers will be more readily linked to specific genetic loci. In this article, we describe the main phenotypes of neuro-anatomic measurements that are widely used in research, and report data on their heritability in the general population. Then, we focus on the results of the few structural neuro-imaging studies that have been carried out in families of patients suffering of bipolar disorders. The current data converge to indicate that subtle structural abnormalities, particularly at the level white matter tracts, seem to be promising endophenotype candidates for bipolar disorder.