Cats can inherit or develop disabilities, just like humans. Blind or mobility-impaired cats are easy to spot. Deaf cats aren't always easy to spot. Healthy cats don't necessarily recognize words or know that they have names, and cats who've learned that humans call them for reasons that may not fit into the cats' agendas may ignore their humans' calls...but if a cat ignores the sound of the can opener, rustling sack, or other audible indications of mealtime, the cat may be losing its hearing. Deaf cats are at a tremendous disadvantage outdoors and need to be kept indoors.
Cats can also have brain damage. AC readers who've found me here have been introduced to the Patchnose Family, by now an extended family of very social, intelligent cats rescued from the streets of Kingsport, Tennessee. When I met these cats, although they were beautiful, clever, and friendly, they were infected with worms, fleas, and fleaborne diseases. Patchnose, the feral mother cat, died shortly after her younger kittens started eating solid food. The older kittens "mothered" the babies, but two of the three younger kittens seemed damaged. They matured slowly and didn't pass the developmental milestones the older kittens did. They weren't as clever or as well coordinated as normal cats.
I let one of these damaged kittens, Graymina, have kittens of her own...which, because these cats are so social, seemed to have been a traumatic mistake for the whole family. Graymina had no instinct to hide the kittens in a safe place when they were born, and lost at least one by failing to remove the placenta after dropping it in the front yard. Apparently her siblings had to help her hide the kittens while she was nursing them, and start to wean them about a week after a normal cat would have started weaning them. Surprisingly, one of her kittens did survive to an adoptable age, but he wasn't a normal kitten either.
Possibly this unfortunate cat had learned something, and might have been a better mother to another litter, but I didn't want to take the chance. She was a sweet, pretty little fluffbrain who needed lots of protection, and she became a nice indoor pillow substitute for some city-type cat owners.