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.
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
Can Dogs Have Autism ?
As early as 1966, veterinarians were talking about the occurrence of autism-like symptoms in dogs. More recently, a presentation at the 2015 American College of Veterinary Behaviorists reported on investigations into tail chasing behavior in Bull Terriers and a possible link to autism. The study included observations of specific traits and DNA analysis of 132 Bull Terriers; 55 tail chasing and 77 control (non tail-chasing). The researchers found that tail chasing is:
a) more prevalent in males,
b) associated with trancelike behavior, and
c) episodic aggression (which was violent and explosive) (Moon-Fanelli et al. 2011).
These findings, coupled with the repetitive motor behavior of the tail-chasing behavior and a tendency for phobias, led us to conclude that tail chasing could represent a canine form of autism.
Diagnosing Autism in Dogs
Studies like this one indicate that autism could very well occur in dogs. But, it’s important to acknowledge that until more research is done, reaching a definitive diagnosis in an individual dog is anything but straightforward. Our understanding of typical and atypical canine behavior is simply too limited. Also, a number of other difficult-to-diagnose canine conditions (e.g., anxiety disorders and pain) can cause clinical signs similar to those associated with autism. Therefore, in all but a few exceptional cases, like the Bull Terriers mentioned above, the best veterinarians and owners can do for now is to say a dog might have autism.
For a dog to be tentatively diagnosed with autism, he or she should exhibit atypical repetitive behaviors and some degree of impaired social interaction with dogs and/or people. Also, a veterinarian must first rule out other conditions that might be responsible for the observed clinical signs.