By Jennifer Coates, DVM
Anyone who has spent enough time around dogs understands the compatibility between the canine and human species. To paraphrase Forrest Gump, we “goes together like peas and carrots.” What makes the human-dog partnership so perfect is our unique combination of similarities and differences.
But sometimes our similarities have a dark side—like the diseases that affect both dogs and people. These include certain types of cancer, diabetes, epilepsy, and congestive heart failure to name just a few. Down syndrome is a common chromosomal abnormality in people. The question that naturally follows is “Can dogs have Down syndrome?”
What is Down Syndrome?
To answer that question, we first have to understand what Down syndrome is. The National Down Syndrome Society provides a good explanation:
In every cell in the human body there is a nucleus, where genetic material is stored in genes. Genes carry the codes responsible for all of our inherited traits and are grouped along rod-like structures called chromosomes. Typically, the nucleus of each cell contains 23 pairs of chromosomes, half of which are inherited from each parent. Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21.
What Are the Symptoms of Down Syndrome?
The presence of this extra genetic material can have a wide range of effects. People with Down syndrome have some degree of intellectual impairment, but this can vary widely between individuals. According the US Centers for Disease Control and Prevention (CDC), some of the common physical features of Down syndrome include:
- A flattened face, especially the bridge of the nose
- Almond-shaped eyes that slant up
- A short neck
- Small ears
- A tongue that tends to stick out of the mouth
- Tiny white spots on the iris (colored part) of the eye
- Small hands and feet
- A single line across the palm of the hand (palmar crease)
- Small pinky fingers that sometimes curve toward the thumb
- Poor muscle tone or loose joints
- Shorter in height as children and adults
People with Down syndrome may also have a range of medical problems. The CDC reports these as the most common:
- Hearing loss (up to 75% of people with Down syndrome may be affected)
- Obstructive sleep apnea, which is a condition where the person’s breathing temporarily stops while asleep (between 50 -75%)
- Ear infections (between 50 -70%)
- Eye diseases (up to 60%), like cataracts and eye issues requiring glasses
- Heart defects present at birth (50%)
Can Dogs Have Down Syndrome?
Determining whether dogs can have Down syndrome depends on how you look at the question. The CDC estimates that about 1 in every 700 babies born in the United States has Down syndrome. The same certainly can’t be said about dogs. If Down syndrome does occur in dogs, it is a much rarer event.
Genetically, dogs and people have many similarities but important differences obviously do exist. For example, people have 23 sets of chromosomes while dogs have 39. Therefore, duplication of all or part of chromosome 21 would have different effects in the two species. Interestingly though, scientists are using genetically engineered mice as animal models in Down syndrome research. These mice carry an extra portion of their chromosome 16, which carries genes comparable to those included on human chromosome 21. The result is a mouse who has some characteristics similar to human Down syndrome. Keep in mind, however, that these are not naturally occurring mice; they have been genetically engineered.
Even expanding the definition of canine Down syndrome to include any genetic duplication that results in clinical abnormalities similar to those seen in people with Down syndrome, the condition simply has not been described in dogs. Three explanations are possible:
- These types of chromosomal abnormalities typically lead to early death in dogs.
- The genetic testing needed to identify dogs with Down syndrome simply isn’t done.
- The condition truly doesn’t exist.
Conditions that Look Like Down Syndrome in Dogs
On the other hand, congenital or developmental conditions are routinely diagnosed in dogs that have some clinical similarities with Down syndrome. Congenital hypothyroidism is a good example. It is caused by low or absent levels of thyroid hormone at birth and early in life, which results in some combination of the following:
- Slow growth eventually resulting in small stature
- Broad head
- Large, protruding tongue
- Short limbs
- Abnormal gait
- Poor muscle tone
- Mental dullness
- Delayed opening of the eyes and ears
- Delayed tooth eruption
Other conditions that could be confused with Down syndrome in dogs include pituitary dwarfism, congenital hydrocephalus, growth hormone deficiency, and portosystemic shunt.
If you think that your dog could have a condition like Down syndrome, talk to your veterinarian. He or she can recommend an appropriate diagnostic plan and make treatment recommendations once a diagnosis is in place.