The Facts

    Each person has genes that are composed of strands of DNA.  DNA is made up of 23 pairs of chromosomes (22 autosomes, 1 sex chromosome). Our genes hold the hereditary information passed down from our parents.  Half of the genes come from the mother, and half come from the father. So a person has 50% of their genes similar to their mother, 50% similar to their father, 100% similar to an identical twin, and 50% similar to a fraternal twin or other sibling.  If identical twins share 100% of the same genes then you would think that if one twin had bipolar disorder the other twin would have it too.  Fortunately, this is not true.  In bipolar disorder if one identical twin has bipolar disorder the other twin has almost 60% chance of having it too.  This is still a very large percentage, which is the reason so much research has been done in order to have a better understanding of the role of genes in people with bipolar disorder.  A better understanding can lead to further improvement of treatment and for identifying those at risk.  A fraternal twin has a 12% chance of having bipolar disorder if the other twin has it. (Millon, Blaney, & Davis, 1999)

The role genetics plays in determining Bipolar Disorder has been an area of interest for a long time.  Bipolar Disorder and Schizophrenia are two disorders that are thought to be highly genetic.  It is important to note that Bipolar Disorder is not believed to be caused by genes alone, but many people are more susceptible to the disorder if someone in their family (especially a parent or a sibling) is already diagnosed with it.  Environmental factors such as stress or disease can cause the disorder to develop if you are already vulnerable for it because of your genes.

Genetic Studies

     Many studies have been conducted in order to try and pinpoint how genes play a role in Bipolar Disorder.  Adoption studies, twin studies, family studies, linkage studies, and association studies are all examples of ways researchers are using to find out more about bipolar disorder amongst relatives.  The findings from these studies suggest that close blood relatives of individuals who have bipolar disorder are much more likely to suffer from those conditions than members of the general population.  Adoption, twin, and family studies report larger results, while association and linkage studies' results are minimal. Advances in molecular biology make it more possible to find the potential susceptibility genes for bipolar disorder.

 Adoption Studies show the concordance rate of the disorder between the adoptee and adoptive parent.  Then it compares that rate to the concordance rate of the disorder between the adoptee and their biological parents.

 Twin Studies  research the concordance rate of the disorder between identical twins and fraternal twins.

Family Studies concentrate on records of many generations of a family.

Linkage Studies  show an association between two or more genes where the traits they control tend to be inherited together. This type of study pinpoints the chromosomal location of a gene that causes the manifested trait.

 Association Studies  aim at demonstrating a significantly different distribution of gene variants (alleles) in control and affected populations.

"Genetic research in mood disorders can be reasonably expected to contribute in the following areas associated with treatment effects:
    1.  prediction of treatment response in individual patients;
    2. prediction of side effects and optimization of treatment;
    3. identification of homogeneous clinical populations for biological/genetic studies;
    4. better understanding of the mechanisms of the illness;
    5. better understanding of the nature of treatment response that can lead to a development of new treatments, possibly including gene therapy (Alda M., 2001)."

**To look up genetic terms go to -->Genetic Glossary