Bipolar Disorder inheritance
At first, the general opinion of the causes of manic depression was pointed at the way the children were raised. In time studies have shown that the way children are raised is not the issue. Nowadays the popular cause tossed around is genetics. This means that children whose parents had history of manic depression have greater chance to develop it themselves.
To confirm this, scientists went a step further and turned to adoption and twin studies.
In case of adoptions, it turned out that regardless of the treatment the children had from their adopted parents, they still have increased risk of developing bipolar disorder like their biological parents. This ruled out the theory about bad parenting being the issue. Twin studies compared results in cases of both identical and fraternal twins. Identical twins share all their genes, fraternal twins share about half of their genes like siblings do. If one identical twin was affected by bipolar disorder, the other one has between 60 and 80% chance of being affected. In case of fraternal twins the odds are about 20%. These studies together indicate that genes do have a part to play in bipolar disorder. Another result that came out of these studies is that a certain environmental effect influences the people who have no genetic predisposition to be affected.
So the studies have confirmed that certain people have genetic predisposition to be affected by manic depression, but whether they do or not seems to depend on other factors.
For people interested in finding out more about bipolar disorder genetics in their family can contact a genetic counsellor’s services.
Linkage Analysis - looking for the diseased gene
Linkage analysis collects blood samples from families whose members are known to have certain disease. These samples can help scientists to trace parts of chromosomes inherited through generations. Chromosomes consist out of genetic information inherited from generation to generation or DNA. For example, a large family is descended from a great grandfather with bipolar disorder. His descendants affected with bipolar disorder will have the exact part of a certain chromosome. The ones without bipolar disorder will not. This leads to a conclusion that a specific part of that certain chromosome is carrying the gene that causes bipolar disease in the family.
The problem begins with the notion that bipolar disorder may be caused by many different genes, or even combination of several genes. Linkage studies have to assume a lot of various factors such as how many copies of a carrier gene and so on. Multitude of these factors leaves a lot of room for assumptions.
The fact that remains is that to this day, each time scientists seem to have found evidence of particular chromosome being linked to bipolar disorder, they were unable to confirm results.