Clinical depression and bipolar disorder have a g common gene variation:
Whether major mood disorders, such as bipolar disorder and clinical depression, are the result of heritage or environmental factors has been a point of contention for some time now. Studies in the recent past have encountered difficulties mapping the differences in the genetic profiles between those affected by individual major mood disorders and others who are not. A new meta-analysis in Nature has widened the scope of study by looking at two major mood disorders at once, and by doing so, have found that individuals with either disorder tend to carry a certain allele on the same gene.
Similarities between major mood disorders, such as treatments, shared familial risk, and the concordance of a disorder between sets of twins, are considered to be evidence that the major mood disorders arise from at least some similar genetic factors. Studies done on major mood disorders typically concern themselves with one disorder at a time, such as major depressive disorder, but often don’t turn up conclusive evidence about which genes might be causing problems.