There isn't a breed that is called a 'Teacup'. What you are actually buying is a cat that is smaller than the norm and is what is called the runt of the litter.

Now not so long ago (before the crazy fad of so-called designer cats and dogs) these runts were virtually given away when they appeared in a litter as being small and weak meant they had the potential for ongoing health problems. They certainly were never considered the best specimens for adding to a breeding programme by any reputable breeder.

Breeders that advertise these Teacups are anything but reputable as they are breeding for the high price these cats seem to fetch, not for their health.