Down Syndrome in Dogs

There are many similarities we can find between humans and dogs; specifically, at the disease level, dogs can suffer from many of the conditions we humans experience. But can dogs have Down syndrome?

Science has shown that, besides humans, chimpanzees can also have Down syndrome, but when it comes to four-legged pets like dogs, there's still no satisfactory evidence. Let's take a detailed look at whether it's possible for a dog to have this syndrome.

What Is Down Syndrome?

Before digging into whether dogs can or can't have Down syndrome, we first need to understand what Down syndrome is.

Down syndrome is a genetic disorder that occurs when abnormal cell division produces an extra copy of chromosome 21. This additional genetic material causes the physical characteristics typical of this syndrome.

Our genetic material is organized into paired packages called chromosomes, and people have 23 pairs, meaning a total of 46 chromosomes. In Down syndrome, there's an additional copy of chromosome 21, so at this level there are 3 chromosomes instead of 2 (trisomy 21).

An extra chromosome, beyond the expected 46, generally results in an embryo that can't develop, leading to miscarriage. However, in the case of chromosome 21, since it's smaller, an extra copy of the chromosome can result in an embryo that survives and a baby being born, though this baby will have a set of atypical physical characteristics.

Can Dogs Have Down Syndrome?

Dogs' genetic material is also organized into chromosomes, but the number of pairs is different from humans'. Dogs have 78 chromosomes compared to the 46 we humans have, and their pair 21 doesn't contain the same information as ours, so trisomy 21 in dogs wouldn't cause Down syndrome.

However, much of the information found on pair 21 in humans does appear elsewhere in dogs' chromosomes. So, dogs could experience chromosomal trisomies in pairs other than 21, which could lead to physical abnormalities and cognitive difficulties, but these wouldn't be Down syndrome as such.

This is why the answer to whether dogs can have Down syndrome can be somewhat confusing, but if we stick to the exact definition of this condition, dogs couldn't suffer from this syndrome.

In addition, due to the process of natural selection, in cases where dog embryos with some trisomy do reach birth, their survival would be very difficult — the mother usually rejects them after birth, or their condition is incompatible with life, and they end up dying within a few days of being born. This is why it's very hard to find cases of dogs with this type of genetic abnormality.

Conditions With Symptoms Similar to Down Syndrome in Dogs

Although it's possible for genetic abnormalities to produce symptoms similar to Down syndrome, there are more common congenital or developmental conditions in dogs that also share clinical similarities with Down syndrome.

Congenital hypothyroidism is a good example. This condition is caused by low or absent thyroid hormone levels at birth or in early life, resulting in symptoms such as slow growth, short legs, a wide head, a large tongue protruding from the mouth, delayed opening of the puppy's eyes and ears, delayed tooth eruption, reduced muscle tone, mental dullness, and gait disturbances.

Other conditions that could be confused with Down syndrome in dogs are congenital hydrocephalus, pituitary dwarfism, growth hormone deficiency, and portosystemic shunt.

Because of this, if we detect symptoms similar to Down syndrome in our dog, we need to see the vet, since, although there's no "official" diagnosis of Down syndrome for dogs, symptoms resembling Down syndrome in humans could point to other health problems, like the ones we've seen above.