By hannah hollinger
Published: 07/19/2017, edited: 09/09/2021
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Both hounds and humans can develop some of the same health conditions, from physical ailments such as cardiovascular disease and arthritis to mental illnesses like anxiety and depression.
Just like humans, dogs can also inherit chromosomal conditions that are similar to Down Syndrome. Keep reading to find out what causes Down Syndrome in humans, whether dogs can develop Down Syndrome, and how chromosomal conditions are diagnosed and treated in dogs.
What is Down Syndrome?
Down Syndrome is a congenital chromosomal condition, which means it's present at birth. This condition is caused by an extra copy of chromosome 21, which affects cognitive and physical development. People with Down Syndrome also have a higher risk of developing other health conditions, including heart disease and Alzheimer's.
Did you know there are actually three subtypes of Down Syndrome? These are called trisomy 21, translocation, and mosaicism.
But before we dive into the different types of Down Syndrome and their causes, let's look at how chromosomes work. Chromosomes essentially condense our DNA molecules so they can fit inside our cells. Our chromosomes determine everything from our physical appearance to our disposition for developing certain diseases. Humans have 23 pairs of chromosomes. Ordinarily, we inherit one copy of each chromosome from our parents. People with Down Syndrome have a third full or partial copy of chromosome 21.
Humans with the trisomy 21 variation of Down Syndrome, which is the most common, inherit two copies of chromosome 21 from one of their parents. This happens when the pair doesn't separate normally within the egg or the sperm before or during conception. Current research suggests that this error most commonly occurs in the egg.
Translocation occurs when the extra copy of chromosome 21 attaches to another chromosome. Curiously, this chromosome is most often chromosome 14. Translocation accounts for about 4% of cases of Down Syndrome.
The rarest form of Down Syndrome is called mosaicism. This occurs when the extra copy of chromosome 21 doesn't replicate in all cells. As a result, some cells have the usual 46 chromosomes, while others have 47. People with this form of Down Syndrome may not exhibit the same clinical signs as those with trisomy 21.
Can dogs get Down Syndrome?
Now that you know how Down Syndrome develops in humans, you might be wondering, "Can dogs get Down Syndrome?"
Currently, the answer is no. Some sources claim the answer isn't straightforward; however, there's no scientific evidence to prove that Down Syndrome, as we know it in humans, also exists in dogs.
That said, certain health conditions in canines can mimic Down Syndrome. These include:
- Pituitary dwarfism. This autosomal disorder is caused by a deficiency of the growth hormone. Aside from a small physical stature, dogs with pituitary dwarfism suffer from an array of health conditions, including kidney failure. This condition most often occurs in German Shepherds and certain wolf hybrid breeds.
- Congenital heart disease. Causes of this rare disease vary; genetics and environmental factors may play a role. Symptoms will vary depending on the defect.
- Hypothyroidism. Although it's rare, dogs can inherit this disease from their parents. Symptoms may mimic those of Down Syndrome, particularly regarding organ formation and function as well as metabolism.
Finally, it's important to note that veterinary genetics is an evolving field. Although veterinary geneticists have studied the canine genome extensively and discovered more than 300 genetic diseases, we do not yet understand canine genetics as fully as we understand the human genome.
How is Down Syndrome similar in dogs and humans?
Dogs can develop chromosomal conditions just like humans, and some of the clinical signs of those conditions are similar to those of Down Syndrome. A few of these include:
- Smaller than average face and/or head
- Delayed muscular growth and cognitive development
- Poor eyesight and/or hearing
- Physical deformities, such as short legs
How is Down Syndrome different in dogs and humans?
For starters, canines have 38 pairs of chromosomes. This means that, in dogs, chromosome 21 has different functions and carries different genes. Chromosomal conditions are also thought to be rarer in dogs.
Humans with Down Syndrome often enjoy a high quality of life. Unfortunately, the same can't typically be said for dogs suffering from chromosomal abnormalities. Tragically, many dogs with such conditions often die before birth or shortly after. Those who do survive often suffer from pain associated with malformed organs in addition to the symptoms above. Some dogs with chromosomal conditions may be unable to eat.
How are chromosomal conditions like Down Syndrome in dogs diagnosed and treated?
Because genetic testing is typically only available at specialized facilities, it will be difficult to confirm if your dog has a chromosomal abnormality.
Since chromosomal abrnomalities are congenital, unfortunately, there is no cure. Your veterinarian will conduct a physical examination to determine if your dog has special needs. Make sure to notify your vet of any clinical signs you've observed and follow their instructions carefully. Most often, treatment will be palliative, or done to ease the dog's pain and improve their quality of life as much as possible rather than to cure the condition.
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