Well. The honest truth is that they're considerably more susceptible to hypertrophic cardiomyopathy (HCM), and hence much more likely to die early from congestive heart failure. The same breeding that has reinforced the hairless genes has also reinforced a genetic predisposition to heart issues. (FWIW, heart disease kills a lot of cats across the board, but it's more common in specific breeds.) As far as I can tell, they're on-par with Maine Coon cats in regards to the prevalence of HCM, but not quite as bad as Ragdolls (which are about 1:4)

Aside from that, Sphnyx tend to get a lot of ear wax buildup that needs to be manually cleaned because they lack cilia in their ears. They also need to be bathed regularly, since their tongue doesn't work well for cleaning skin, and they can get pretty grungy. They seem to be slightly more prone to having sensitive stomachs.

Otherwise, they tend to be very friendly, active, people-oriented cats.

We've had a total of 6, but have lost two to heart failure, with two more that are in the very early stages of heart failure, all at under 8 years old.