Molecular Genetics of Bipolar Disorder

Abstract

Bipolar disorder (BPD) is a disease of unknown etiology, which is a major cause of disability. The disease is characterised by oscillation between a manic state and a depressed state, and has a significant genetic component. To try to improve understanding of the disease, linkage studies and association studies have been conducted on bipolar subjects. To date these studies have yielded equivocal results. A very small number of genomic regions and genes have been identified which are associated with the bipolar disease. This small number of genes does not explain the high heritability of the disease. Using the results of these screens as starting points it should prove possible to develop a model for the underlying molecular components of BPD. Key Concepts: Bipolar disorder is a highly heritable psychiatric disorder where genetics are proving to be complex. Psychiatric linkage studies have been less successful than genome wide association studies at showing involvement of genes in psychiatric disease. Genome wide association studies can provide information about genes that are involved in a disorder. Not all of the heritability of bipolar disorder has been explained by genetic association studies. The nature of this ‘missing heritability’ remains unclear. Genetic modifiers are genes that can alter the phenotype caused by a mutation. These genetic modifiers may account for some of the missing heritability seen in bipolar disorder.

Neuroanatomical alterations in brain disorder: A magnetic resonance imaging analysis

“…The heritability of bipolar disorder is a measurement of the degree to which the variability of the trait may be attributed to genetic factors. There is a sizable heritable factor for mental disorders, ranging between 60% and 80% (6). Although predictions that members of the second-degree relatives had an increased risk in depression, an additional study has shown the risk of unipolar disorder in second-degree relatives is comparable with that of the population as a whole (7).…”