Can Cats Have Down Syndrome?
Every year, about 6,000 babies in the United States are born with Down syndrome, a chromosomal condition marked by traits like cognitive challenges, shortened stature, a flattened face, and hearing loss.
Down syndrome is a relatively common diagnosis in the human population. But if you’re a feline parent, you may be wondering: can cats have down syndrome?
Here, we answer that question, plus provide insights into what may be at the center of your cat’s unique characteristics. As always, it’s best to contact your veterinarian if your cat is displaying any unusual signs.
What is Down Syndrome?
Down syndrome is a chromosomal condition that most often occurs when there’s an error during cell division. The medical term for this prevalent form of Down syndrome is called Trisomy 21 (or nondisjunction).
Each cell in the human body typically contains 23 pairs of chromosomes. Most children born with Down syndrome, however, have three copies of Chromosome 21.
“The fetus gets three of these chromosomes when the egg is fertilized, rather than one from the egg and one from the sperm. The upshot is that either the egg or the sperm carried an extra Chromosome 21,” explains Dr. Liz Stelow, a board-certified veterinary behaviorist and chief of service of clinical behavior service at the University of California, Davis Veterinary Medical Teaching Hospital.
Instead of the typical 46 chromosomes, the cells of people with Down syndrome contain 47. Scientists theorize that the extra genes on Chromosome 21 disrupt how genetic information is decoded.
People with Down syndrome vary in their abilities and personalities, just as you’d expect in the general population. Common characteristics of the condition – which are present in varying degrees – include learning challenges, slower speech, a flattened face, slanted eyes, a short neck, small ears, low muscle tone, and a shorter stature.
Can Cats Have Down Syndrome?
The short answer is that Down syndrome in cats doesn’t exist. In humans, the condition is most commonly the result of an extra copy of Chromosome 21. Given that cats have just 19 pairs of chromosomes, they can’t have Trisomy 21.
There are, however, genetic mutations that can cause traits similar to those found in people with Down syndrome, says Dr. Sasha Gibbons, an associate veterinarian at Just Cats Veterinary Hospital in Stamford, Connecticut. “But the etiology (cause) of these changes are slightly different than that of people.”
An example is the mutation linked to the UDP-glucose 6-dehydrogenase (UGDH gene), which results in the shortened legs in the Munchkin cat breed.
Can Other Animals Have Down Syndrome?
Even if cats and other animal species could acquire three copies of Chromosome 21, their genes are structured differently than ours. This means that any condition or disease, if present, would be expressed uniquely.
Though Down syndrome is a human condition, there are interesting genetic similarities to Trisomy 21 found in the animal kingdom.
Mice
Mice have 20 chromosomes and are unable to develop Trisomy 21, but there are similarities between human Chromosome 21 and mouse Chromosome 16. Mice with Trisomy 16 exhibit learning difficulties.
More recently, mice who received an inserted copy of human Chromosome 21 have displayed characteristics consistent with Down syndrome in humans – including learning challenges, a greater risk for heart defects, and a marked facial structure.
Chimpanzees
Chromosome 22 (of 24 pairs) in chimpanzees is structurally similar to human Chromosome 21. To date, scientists have identified two chimpanzees with Trisomy 22, including one with a shorter stature and a prevalence for heart disease, and who developed cataracts at a young age.
Cat Conditions That May Be Confused With Down Syndrome
While there’s no such phenomenon as a Down syndrome cat, some felines exhibit traits and behaviors – like a broad face, short stature, and poor muscle tone – that mimic those in people with the condition.
So, if Down syndrome in cats doesn’t exist, then what’s behind these traits? The following conditions may help explain what’s going on with your kitty. Always contact your veterinarian if you suspect something is amiss.
Cerebellar Hypoplasia
Cerebellar hypoplasia is a condition where the brain’s cerebellum fails to fully develop. It’s often brought on by the distemper virus infection (panleukopenia) that occurs during pregnancy, says Dr. Drew Weigner, past president of EveryCat Health Foundation. It “causes incoordination and tremors in affected kittens who appear otherwise normal.”
Hydrocephalus
Hydrocephalus is a birth defect that causes liquid in the brain to accumulate, says Dr. Weigner, who says that it results in “an enlarged head and neurologic symptoms.” Cats with hydrocephalus may also have a larger skull, a downward gaze, seizures, blindness, and a propensity to walk in circles.
Seizures
According to Dr. Gibbons, seizure disorders that result in brain damage could cause symptoms similar to Down syndrome, such as “slower-than-normal nerve reflexes, and the appearance of lower-than-average intelligence.”
Head and Facial Trauma
A cat who’s had an accident at a very young age can develop head or face trauma, which Dr. Weigner says “can affect their appearance and coordination.”
Toxins
What seems like a cat with Down syndrome may actually be signs of exposure to lead and insecticides. Dr. Weigner notes that this can result in neurologic symptoms in cats. Certain flowers like lilies and foods like grapes and chocolate can also cause a range of unwanted symptoms, including lethargy and weakness.
Dysautonomia
Dysautonomia – the degeneration of nerve cells – presents signs similar to Down syndrome, says Dr. Weigner. Signs of feline dysautonomia include mental dullness and unresponsive pupils.
Eyelid Agenesis
Eyelid agenesis is a birth defect that can result in a flattened face or almond-shaped eyes, according to Dr. Gibbons. “That would give an appearance to cats that could resemble a human with Down syndrome.”
Strabismus
Cats with strabismus have eyes that appear crossed. “While they’re otherwise normal, they can be somewhat clumsy because, well, they’re cross-eyed,” says Dr. Weigner.
Chromosomal Abnormalities in Cats
It’s important to note that not every cat who looks or behaves differently has a chromosomal abnormality. “More commonly, certain behavioral abnormalities, such as wool sucking, or compulsive ingestion of wool in clothing, is associated with certain breeds, in this case in Siamese cats. But that doesn’t mean their genes are abnormal,” says Dr. Weigner.
Gene mutations do occur in cats, however, and they can cause health issues. One breed-specific genetic mutation called Burmese head defect causes a malformed skull and face. “Unfortunately, it’s usually fatal and these kittens don’t survive long after birth. There’s now a genetic test that detects carriers of this abnormality so they’re not used for breeding,” Dr. Weigner explains.
Though any form of trisomy (a third copy of a chromosome) in cats is considered rare, Dr. Stelow notes the exception is XXY trisomy, which results in a sterile male. “This is the feline equivalent of human Klinefelter syndrome and is the explanation for calico or tortoiseshell male cats.”
Female cats can acquire a rare single X chromosome that’s similar to Turner’s syndrome in humans, which Dr. Stelow says can lead to aggression issues.
Feline Genetic Research
Though Down syndrome in cats may not be a recognized condition in the veterinary community, scientists have been studying how gene abnormalities contribute to other conditions and diseases.
One of these efforts is the Feline Genome Project at the Feline Genetics and Comparative Medicine Laboratory, University of Missouri in Columbia. The Project consists of scientists working to compile DNA sequencing in the cat genome, similar in scope to the Human Genome Project. Identifying gene mutations that cause disease can ultimately aid in improving cat health. If you’d like to participate, the Feline Genome accepts volunteer samples of cat DNA from the public.
In another recent large-scale study of more than 11,000 cats, researchers sought to identify genetic variants that cause diseases, as well as their frequency in both pedigreed and non-pedigreed cats. They’ve been able to identify 13 new gene variants linked to diseases in 47 breeds and found that three of these are unique to non-pedigreed cats. As with the Feline Genome Project, these types of studies provide information that can ultimately benefit the health and welfare of cats.
