Posted by sunnydays on May 11, 2007, at 16:25:05
In reply to Re: Bi Polar/Recurrent Unipolar and Antidepressants!!!, posted by linkadge on May 11, 2007, at 13:17:40
> I don't know how they would come to that conclusion seeing as nobody has descovered a single gene that accounts for all of the current manifestations of depression. Even some of the so called *candidate* genes are only showing up in a small fraction of those diagnosed with depression.
Depression is a complex disorder just like heart disease, as such, no single gene will account for all manifestations - different genes contribute to susceptibility. Complex disorders are also influenced by environmental factors, so many of the genes that influence them have absolutely no effect without specific environmental factors being present.
The locus I was thinking of that has similar effects in depression and bipolar is called 5-HTTPR. The short allele of this gene is correlated with depression if a person experiences significant stress early in life or more recently. It is also associated with taking longer to respond to SSRIs and with poorer response overall to SSRIs. The short allele has also been found to be associated with nonresponse to lithium prophylaxis in those diagnosed with bipolar I. Lithium is thought to affect the serotonergic system, although the exact mechanism is not known, so it seems depression and bipolar can both be treated with drugs that affect the serotonin system and this gene also affects that system and seems to contribute to at least some of the symptoms of those disorders.
Again, it is important to understand that NO single gene will account for all of the cases of ANY disease or disorder at all except for the simply inherited Mendelian disorders. Depression and bipolar are not Mendelian. Looking for a single gene to explain everything is a common misunderstanding of how genetics works in both the popular media and among many individuals.
Hope this explains what I meant when I made that statement.