I have seen a few genuine MDD with psychotic fx, but like everyone's already said, most are actually either on the Borderline Spectrum or simply colloquialize a strong intrusive (but self-voiced) thought as 'a voice'.
Most of the MDD with psychotic fx I've seen has been in people with a family history of BPAD and/or schizophrenia. Which makes sense, when you think about it.
As for the genetics, etc. I do think that there is some splitting apart left to do, but I also think that since we actually only understand the mechanics of all of our disorders in the crudest sense, most likely we will eventually discover that while multiple genes contribute, they mostly do so through distorting or derailing a common single pathway, rather than multiple pathways that 'look the same'. A situation more analagous to the genetics and pathophysiology of DM2 (ultimately it's all insulin resistance) rather than Ventricular Tachycardia for instance.
BTW, Ceke, I haven't had a chance to say this yet, but you are definitely a blessing to the forum. Total score for all of us to have your point of view available.
First of all, thank you for your kind comment. You have me blushing over here.
Now I need to tread carefully with this reply, because I'm not supposed to discuss my own diagnosis in too much detail lest it seem I'm angling for medical advice. It's interesting the mention of family history. Most of the people I've spoken to who 'thought' they had MDD with Psychotic Fx (because this one time they were stressed out and felt really down, and then they saw shadow creatures out the corner of their eyes so now they're totes psychotic as well as being depressed because that HAD to be an hallucination - I'm sure you've heard the same lyrics sung to a different tune) when spending even five minutes speaking to them, even as a lay person, it was pretty clear they nowhere near met diagnostic criteria, absolutely none of them reported any history of Schizophrenia or Psychotic spectrum disorders in their family, but there was always plenty of anxiety and anxiety related disorders. Me personally, I had one Great Aunt, on my Dad's side, who was institutionalised for life in an Insane Asylum back in the 1940s or 50s (the family always referred to it as a Nervous Collapse, but it was pretty clear from later details that emerged through family research it was likely she suffered from Schizophrenia in some form or another), and my Dad wasn't exactly what you'd call normal in terms of thought processing either (he had hallucinations of dancing mice on the TV, thought a 'Doctor's Mafia' existed to put hits out on patients if they made any complaints, and regularly checked the garden for hidden listening devices). So yeah, family history, definitely in my situation.
Having said that, although I no longer meet specific diagnostic criteria for any one personality disorder, I do still carry aspects with me, including what I suppose might be referred to as tendencies from the Borderline Paradigm or Spectrum. The thing is though, I can tell the difference between my latent personality disorder, chicken little 'the sky is falling' overreactions that can then lead to a stress induced pseudohallucinatory experience (what I think of as 'soft psychosis) and the types of things I experience associated with MDD with Psychotic Fx. The two things feel very different, to the point that is almost feels like they are coming from different areas of the brain. In my case therapy, mindfulness, yoga, and remaining spiritually aware and focused helps me deal with the personality disorder 'soft psychosis' episodes, the other stuff I hammer away at with medication (especially the expressive dysphasia/word salad/poverty of speech side of things - nothing more frustrating than trying to have a conversation with a loved one only to stammer at them blankly, or open your mouth and have complete gibberish come out)
I hope that wasn't TMI for my situation? Trying to tread very softly, tip toeing even.
So now I'm wondering if anyone else has had a patient with co-morbid diagnosis of Personality Disorder(s) on top of MDD with Psychotic Fx and if they've described similar feelings - ie the idea/thought that the experiences between the two are very different, not just in content, but in actual 'feeling' as well.
