[H]aving a depressed mother substantially ups a teenager’s likelihood of becoming depressed, even if he or she was adopted and shares no genes with the mother. . . .
Having a depressed father does not increase depression susceptibility in either adopted or non-adopted teens . . . successful treatment of depressed mothers — either with medication or psychotherapy — spurs emotional gains in their depressed children.
While living with a depressed mother boosted the mood disorder’s prevalence in adopted teens, non-adopted teens were even more likely to become depressed themselves. For non-adopted teens, genetic influences may amplify as the detrimental effects of environmental factors, the researchers suggest.
Having a depressed mother also increased the rate of delinquency and other behavior problems in both adopted and non-adopted teens.
Neither adopted nor non-adopted teens’ emotional problems triggered depression in their parents[.]
The fact that adoptees with non-depressed mothers did not suffer unusual rates of depression suggests that birth parent depression was not a factor that would impact this result, even though birth parent data was not available.
From here (discussing three recent medical journal articles on the subject).
In previous studies the "heritability of depression—the degree to which it is genetically determined—has been estimated at around 40% for women and 30% for men." But, few studies have done as powerful a job as the one cited above at identifying a statistically significant specific cause for childhood depression in a family setting, apart from genetic influences.
By way of comparison studies have shown "the heritability of risk for schizophrenia to be approximately 80%."
These studies are also notable because they indicate that treatment for depression does work, is not a futile response to a purely genetic condition, and that the benefits can extend beyond the person directly receiving treatment.
The study on the impact of a mother's recovery from depression on her children found that "70 of 123 depressed women recovered from the mood disorder within one year." So, while treatment (a mix of drugs and cognitive-behavioral psychotherapy) isn't a sure cure, most of the time, it works. Cognitive-behavioral psychotherapy also has a good track record of helping children deal with trauma.
Many kinds of treatment help mitigate depression, but while there are differences in observed sucess rates, identifying treatment methods with statistically significant improvement relative to placebos is elusive.
While drug treatment is effective, at least the newest class of anti-depressentants, called SSRIs, like Prozac, Effexor, Serzone and Paxil, "provide an edge over placebos in only the minority of patients with the most severe symptoms." So, "there is little reason to prescribe new-generation antidepressant medications to any but the most severely depressed patients unless alternative treatments have been ineffective."
Depression is among the most common mental health issues, with almost one in twelve Americans experiencing it each year. About one in six people suffer from clinical depression at least once in their life (one in five women, one in seven men). The only mental health conditions similarly common are phobias.
(An interesting manga take on the fallout from one woman's inability to care for her young daughter due to mental health problems is Aishiteruze Baby which was also made into a Japanese television series.)