Há genes da depressão?

A depressão é genética ou deriva de factores ambientais? Provavelmente é uma mistura dos dois. E nem todas as depressões são iguais, assim como o cancro é um nome comum para várias doenças (tipos de cancro), o que torna a resposta à questão especialmente complexa:
http://www.independent.co.uk/life-style/health-and-families/healthy-living/why-is-there-no-gene-for-depression-a7291016.html


Citando:
"So is there a gene for depression? No, there isn’t. We don’t have genes for diseases, we have genes that encode proteins that serve functions in cells. So does that mean if your DNA has the relevant change in your LHPP or SIRT1 genes that you are going to develop depression? No, it probably means you may have an increased risk to develop depression depending on the environment you experience.
In the same way that we think about heart disease, cancer, obesity as having multiple “susceptibility genes”, the same is probably true for depression. "