Cerebellar hypoplasia (video of Amy)

[critters]

As disabilities go, it's pretty common, and it can happen to dogs, too. I don't know that anybody can give you a "x out of 1000 births" guesstimate on it, though. Ari is quite severe.

[smokey the elder]

I've personally observed 3 cats with it, out of about 2,000 or so that I have seen, so maybe 1 in a thousand? (I think diabetes is more common than CH.)