When veterinarians use the term "retardation" in reference to cats, they're generally not referring to cat mental disabilities. They're often talking about impaired physical development instead. In fact, the human concept of "mental retardation" doesn't really apply to cats: We can neither test their intelligence nor even clearly understand their thought processes.
Cat mental disabilities
When a cat appears to be confused, disoriented, or unable to process information as quickly as other cats, the reason isn't necessarily substandard intelligence. Since cats and people suffer from many of the same maladies, such symptoms might suggest almost as many possible causes. Among them are brain damage or other neurological problems, strokes, seizure disorders, genetic abnormalities, and a wide range of viral, infectious and immunological diseases. Only a vet can narrow down the potential causes with the hope of arriving at an accurate diagnosis.
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Genetic mutations, facial deformities, and inbreeding
All cats can inherit diseases if both parents have the same gene mutation, but the likelihood is greater among pedigree cats bred from a restricted gene pool. Some breeds have been created by exploiting existing genetic mutations, which can leave generations more vulnerable to other mutations.
Siamese cats, for example, all carry a mutated gene responsible for partial albinism, which is why they're born white and have blue eyes. That breed is susceptible to the feline version of a genetically transmitted disease that affects humans and causes multiple abnormalities, including facial deformity, in both: Maroteaux-Lamy syndrome, or mucopolysaccharidosis. Even though some people associate facial deformities with mental retardation, cat mental disabilities aren't a symptom of that disease.
Kenny the white tiger
What can happen when cats are inbred for qualities desirable to their owners came vividly to public attention in 2000, after a white tiger named Kenny was rescued by the Turpentine Creek Wildlife Reserve in Eureka Springs, Arkansas. At the time, white tigers fetched exorbitant prices in zoos and among private collectors. But Kenny, who had a severely deformed face and couldn't fully close his mouth, was worthless.
After pictures went viral on the Internet, Kenny started being known as the world's first tiger with Down syndrome. He and his brother Willie, who had orange coloring but crossed eyes, were the offspring of white tiger siblings forced to mate. Kenny died of cancer in 2008 at the age of 10. Whether he was actually afflicted with Down syndrome or any other kind of so-called retardation has never been confirmed.
Cognitive dysfunction syndrome
Cats age nine or older sometimes start to experience a decline in cognitive function called cognitive dysfunction syndrome. CDS is a default diagnosis that vets make when no other disorder can be found to account for behavioral changes such as litter box accidents, uncharacteristic displays of anxiety and general disorientation, and failure to recognize familiar people and places.
Like the brains of people with Alzheimer's disease, the brains of cats afflicted with CDS often show accumulations of a waxy substance called amyloid plaque. Other problems common in aging cats, such as declining heart function causing oxygen deprivation and high blood pressure, can aggravate CDS symptoms.
Retarded physical development in cats
Intestinal parasites such as roundworms and tapeworms can be debilitating enough to stunt the growth of kittens. Abnormalities of the endocrine system such as an underactive thyroid gland — hypothyroidism — can also retard a cat's development. If a pregnant female cat contracts the virus responsible for feline distemper, her kittens are likely to be born with severe brain damage.
Another viral disease, feline leukemia, can cause neurological disorders in adult cats and stunt the growth of kittens. To avoid problems, test your cat for intestinal parasites at least once a year and vaccinate them against viral diseases as appropriate for their age.