Hello BeaFlower,

Such a good question! There are so many schools of thought on it, some people will say it is genetics and others will say not. It's the old nature - nurture debate. Researchers are still looking into it 5 Major Mental Illnesses Traced to Same Genetic Variations | Psych Central News

But I'll give you my opinion. I believe autism is genetic in that it happens while the baby is forming. But for other mental conditions (imho) I believe it is to do with trauma, childhood, life circumstances, stress etc.

It is true that generations can have depression/bipolar etc and it can appear to be genetic, it is more likely that each generation has a sensitivity and the same ways of coping with mental health have been passed down to each generation.

You asked specifically about OCD. OCD can be part of other illnesses such as autism or ADD. OCD in my opinion is provoked by anxiety, that is to say that the rituals are carried out to make the anxiety (fear) feel safe. All about OCD here >>> Obssessive-Compulsive Disorder Symptoms and Treatment So OCD has a very close relationship with anxiety. I do not think that OCD is genetic though it can appear to run in families as a learnt behaviour in trying to cope with anxiety.

Stress, in my opinion has a lot to answer for!

I am sure there will be other people that will disagree with what I have said, as the nature/nurture debate still continues as we still learn about the human mind.