Genetics does not work that way.) Behavior straight out of genes, without social and environmental conditioning is bullshit. Behavior is product of training and acquired habits, guided by hard-wired instincts and emotions.
There might be some predispositions - mutations which introduce minor changes (there cannot be major ones - changes must be small and gradual enough for the organizm to cope with) into some locations, which affect sensitivity to certain chemical compound (hormones, neurotransmitters) or minor structural changes which affects metabolism, but all this could be easily compensated by behavioral patterns on a higher level.
Animals and people with sudden traumas leading to disability are doing this, but way too sophisticated, self-obsessed hipstes and couch potatoes cannot.
Oh, except for all of these: https://en.wikipedia.org/wiki/List_of_genetic_disorders
There are even lots of diseases that provide strange benefits that protect the sufferer from other illnesses. Having half the genes for sickle-cell trait will give you strong resistance to malaria. Having both is a terrible illness. Huntington's Disease seems to provide resistance to certain types of cancers, but when you turn 35 or 40 your life becomes a real nightmare.
The point is that the purpose of genetics is not to promote healthy humans, it's to promote the reproduction of the group of genes in question. Genes will use all kinds of tricky methods to duplicate themselves, including all kinds of things that are awful for the person with them.
What is the experimentaly supported cause of depression, what are the pathological changes, in which areas, caused by which genes?
My point is merely that stating depression can't be genetic because of its negative effects misunderstands genetics, evolution. I'm not saying your conclusion is incorrect- there may not be a genetic component to depression at all- but I am saying your methodology for coming to that conclusion is wrong.
Congratulations on contradicting yourself in two sentences! Or how do you suppose hard-wired instincts are hardwired?