I find that to rather stretch plausibility, not in the least as heterochromia can also be caused by postnatal injuries. And (X) DOUBT @ albinism, leucism etcetera not existing in this world.
It's a manga so suspension of disbelief is kind of necessary. We're already shown things that can't exist in this world so why is it so much of a stretch to assume that there are things in the real world that don't exist in the Catulus world?
Seems like a pretty nonsensical detail to ditch... and I'm not really seeing why the whole thing would have any bearing on pigmentation abnormalities of sometimes VERY diverse origins (one possible cause for heterochromia is genetic mosaicism from a vanishing twin for ex).
It seems to me like a rather more credible explanation that Anna is simply talking out of her ass for whatever reason (she says a fair few dubious-sounding things in general) and/or the author really didn't care about the details making much sense...
It could be that the whole Catulus thing is being retconned by the author as they're prolonging the story.
Can't really disagree here. There's a pretty strong impression of, as it were,
So bounce the graviton particle beam
Off the main deflector dish
That's the way we do things, lad
Making shit up as we wish!
...and it's notoriously hard to keep the whole thing straight (ahem) when writing by the seat of your pants like that.
It's kind of a given an awful lot about the eponymous "syndrome" makes very little sense so it'd arguably be better if the author didn't specifically keep dragging it right into the spotlight where the inevitable holes are that much harder to ignore, tbh.
All I understand so far is that Catulus Syndrome, a condition that is contracted where subjects obtain catlike features as well as the ability to turn into a cat, appears only in girls right around when they hit puberty but there's a rare instance where you're born with it like in Yuki's and perhaps Oguri's cases.
Honestly right now, since it doesn't seem like we've been given the full breakdown of the syndrome, the whole thing just feels like X-Men to me.
Well I think we can assume the condition is genetic at least - if it was contagious the catgirls would hardly be allowed to mingle freely with regular folks, cute or not...
Probably caused by the accumulation of a critical mass of crazy cat ladies over centuries. :U