Is/are Mental Illness Genetic over Environmental Causes?

For a long time I was under the impression that mental illness manifest because of some form of trigger sa environment. Of course may certain mental condition na completely environmental like PTSD (still ... ).

Nagiba na ang pananaw ko, since recently my sister and pamangkin are clinically diagnosed with mental disorders. MDD, and ADHD with Depression and OCD (last two still being further analyzed). Looking back, my other sib also have some form kasi meticolous and very particular na if I asked her to get check she would come out with OCD. We don't have bad parents naman. Typical parents. I personally don't experience trauma specifically. Or what I consider trauma. But who knows.

But it made me consider getting mine checked na din. Self-assessment tests seemed to ranked me as ASD-1. And digging my memory parang my father also has some form din. Since my mom is always complaining about their marital affairs that boiled into resentment, on top of the other trouble with social connecting to people. But I could be wrong sa father ko. He's dead so I could never know.