@Mugen Kagemaru  
Not intentionally! I haven’t read the POV Series, but I’d heard and seen a few things around that made them related, and it seemed like the natural step, since I love making villains sympathetic and miserable.

@Background Pony #6FAD
 
Or maybe it’s a nod to Alex Warlorn’s Pony POV Series

It runs in the family…  
and the family runs from YOU

@redweasel  
Keep in mind, all the ponies in Equestria seem to have varying levels of monomania and a very low threshold for having breakdowns (eg. Lesson Zero, Party of One). This might be like finding out she has an especially weak heart, in a world where everyone’s expected to have 2-3 heart attacks a year.
 
 
@Antonyourknee  
Evolution hasn’t done anything like that for people, so why would it for ponies? And as is the case with any hereditary condition (autism, seizures, baldness, crooked noses…) there are always couples that are willing to gamble that the kids will get the genes from the good side.

I thought Bipolar Disorder, though DT having some mental condition seems to be a popular theory. I wonder how they could work it into the show…

You think evolution would have done its job and the stallions would have stayed far away from the girl with the genetic trait for insanity in them…I suppose Filthy rich was either very dumb or very nice to mate with a mare who’s knows her condition of dementia is hereditary…but then again maybe He’s combing the land for the best docters, trying to cure the aliment however they can.

I kinda like this headcanon. Having Diamond Tiara have this hanging over her head, knowing that one day she’ll end up like her mother and that being one of the things that drives her bad behavior.

schizophrenia is hereditary, but only the predisposition for it. nobody really knows why some family lines are predisposed for it, and some do get dragged into madness for no reason at all, but for most (and schizophrenia is already very rare) they can live long and full lives, and only extremely stressful situations like extreme grief or college will damage their fragile minds.
 
tl;dr dt needs to chill
 
no she will seriously go insane from worrying too much about going insane

@NemoSpecific  
Kinda makes me feel sorry for her. I kinda like versions of Tiara that are more “sympathetic,” yet still a li’l jerk.  
I’d kinda like the show to do something like that, but not make her completely “reformed,” just show a side to her besides, “that li’l brat who nearly destroyed Scootaloo’s confidence.”  
(Some feel Tiara & Spoon became “irredeemable” by that episode alone.)
 
After all, even some “bully/jerk” characters in other old shows like “Salute Your Shorts,” and such have had their likeable/positive moments to.
 
Only canon likeable moment for Tiara (besides some of her cute expressions under the “Diamondbetes” tag) was when she sung briefly, and complimented Pinkie Pie in “Pinkie Pride.” (Though, she did try to steal Silver’s drink, who comically manages to steal it back. I like the implication that they both seem to pick on each other even from that moment.)  
Also, Tiara & Spoon were a li’l nicer in “Twilight Time.” Even if it was mostly brown-nosing, (so they could meet new princess Twilight Sparkle) they were at times during the ep’ trying to help the CMC become more “popular/cooler,” and even let them come to their pool party.

Enjoy the asylum, kid!

@Background Pony #6FAD  
… aaaaaaand now I’m thinking of them as the MLP version of Fight Club. Lovely!

Spoiler: Screwball never existed. She was product of DT’s imagination and her innate chaotic magic.

I’m toying with the idea that not only is Diamond Screwball’s daughter, but that her condition is hereditary. DT has been more than a little stressed out knowing that her mind will disintegrate in twenty years or so, and that’s what causes her to act out.