Achondroplasic Dwarfism in Domestic Animals

To the far right a kitten with achondroplasia stands next to her two standard siblings.
To the far right a kitten with achondroplasia stands next to her two standard siblings.

Introduction

Some people may know about achondroplasia (and hypochondroplasia - the more severe form) because it is the most common form of dwarfism in humans (out of over 100 different varieties of human dwarfism.) It disrupts the process of turning cartilage into bone matter and in doing so typically creates someone with shorter arms and legs an often a larger skull than is usual. Depending on the time period and culture this could be a positive thing (with an invitation for a peasant to join the royal court for example) to a negative thing (with it being classified today as a medical condition.) But achondroplasia is not exclusive to humans by any means. It's a very common genetic mutation among domestic animals and has been used for hundreds, if not thousands, of years to produce an assortment of short domestic creatures. Below I hope to enlighten you with a little history and maybe a touch of scientific knowledge so that you too can understand why we have made this gene into something desirable in our pets and livestock.

Why is Achondroplasia so Common in Animals?

As I stated above there are many things that can cause dwarfism in both people and animals and achondroplasia is just one of them. It's a genetic mutation that has been historically easy to manipulate once it's found in an animal population. The reason for this is because it's a dominant gene which means you only need the original dwarfed animal to create more, as it will likely pass these qualities down to at least some of its offspring, no matter who and what the other parent is. This eliminates the need to breed for several generations to get carriers before getting a baby that expresses the gene in full which is usually how these things go. With that being said you may wonder where the original dwarfed animal comes from. Well, it would come from something called spontaneous mutation. This is when something happens at random in the genes causing things to be slightly different than its parents. For example in cats this could be a curly-haired kitten showing up in a litter bred from two straight-haired parents. If someone takes an interest in the spontaneous mutation (be it achondroplasia or something else) then it can be basis of new breeds being created. Below are some breeds of animals who are perfect examples of this.

Standard Munchkins come in all colors and fur variations.
Standard Munchkins come in all colors and fur variations.
Furless Munchkins are often called Minskins or Bambinos.
Furless Munchkins are often called Minskins or Bambinos.

Achondroplasia in Cats

Currently there is one breed of cat that carries this gene, they're called Munchkins. These cats look more like a ferret with a cat's head than anything. They stand close to the ground with very short legs, and what appears to be their knees are actually their wrists. This breed has been used to make short versions of almost all the other recognized breeds which means there are a lot of people out there that find this trait attractive. The first Munchkin showed up as a spontaneous mutation in a litter of barn cats. He was a male named Blackberry who grew up to have quite the career as a stud sending his short offspring in all directions. At first people didn't know what to think of these new low-riding kitties. There were rumors they were half raccoon. Let me assure you they are 100% feline.

Munchkin breeders normally use both short legged and long legged cats in their breeding program for a variety of reasons. The first is that a kitten that gets a double dose of the gene (one from each short parent) has a pretty high risk of dying during the pregnancy. Although a 25% fetal death rate would be normal in such a breeding it could also be as high as 50% in some cases. These fetuses die early in the pregnancy and are reabsorbed causing litters to be comparatively small. It's also not recommended to inbreed anything quite to that level. Since the breed started with one individual it's good to expand the gene pool a little! And finally crossing the breed with long legged cats is a good way to prevent other tag-along genetic diseases from being locked into the breed.

Introduction to Munchkins

Achondroplasia may may increase the risk of obesity in dogs.
Achondroplasia may may increase the risk of obesity in dogs.
Notice the long spine, deep chest, and shortened legs.
Notice the long spine, deep chest, and shortened legs.
Pekingnese - the tribble of the dog world.
Pekingnese - the tribble of the dog world.
Achondroplasia can cause excessive melting. Just kidding, but seriously it can cause misaligned teeth which are common in English Bulldogs.
Achondroplasia can cause excessive melting. Just kidding, but seriously it can cause misaligned teeth which are common in English Bulldogs.
French Bulldogs are normally born via C-section today as the puppies heads are too big to fit safely through the birth canal.
French Bulldogs are normally born via C-section today as the puppies heads are too big to fit safely through the birth canal.

Achondroplasia in Dogs

I would love to start this section with a story about a breed of dog that's now extinct, the Turnspit Dog, because it's story is so fascinating. At least since the 1500's these dogs were bred to help the servants in the kitchens of royal houses and castles. The dogs were short, bow-legged, with severe expressions and worse temperaments. They were a working dog of the lowliest sort. Before these dogs peasant children were employed to turn spits next to the scorching heat of the fire in order for the meat on the spit to cook evenly but this fell out of practice when someone invented a hamster wheel sort of contraption that they could hook up to the spit. Now instead of peasant children these poor pooches were put into the wheel and made to run for hours at a stretch in the horrendous heat. They were also used as foot warmers during Sunday church services but they seemed to have been rarely if ever kept as pets due to their salty temperaments. I'm not sure I'd be super friendly either if this was my life but this is how it was. And so in the 1800's when mechanical spits were invented these dogs fell along the wayside and quickly became extinct. There is one stuffed specimen and a few illustrations in existence to mark their passing in our history.

With that all being said it may be helpful to know what achondroplasia does to the look of a dog because not all small dogs have this gene by any means. In most it will create short often bowed legs, deep heavy chests, and sometimes they may show up with very large heads, and bulkier heavier bodies. However the gene doesn't effect the growth of the spine so these animals may look elongated and disproportional. Most often these qualities are avoided in working breeds as it may (or may not) cause a dog to run slower, drown under their own weight, be prone to obesity and broken backs, or have trouble birthing puppies. This has caused some breeders to say we should stop breeding them but people still do for all sorts of reasons.

Dachunds are probably the best example. They didn't need to be fast to do their job they just had to be short and fearless as they were originally employed to chase cornered badgers and other animals out of their dens. Corgis were a great way to have a herding dog that didn't need quite as much food as a normal sized herding dog. They were so low to the ground that instead of scaring cattle into their desired corners they nipped at their heals until the job was done. Other dogs to share this gene are Basset Hounds, Pekinese, Shitzus, and English and French Bulldogs as well as some others.

Dachshund Running in Slow Motion

Achondroplasia in Rabbits

Achondroplasia is a bit of a mystery in rabbits. It has been reported as happening at the very least in the Havana breed but it's not seen very often because these dwarfed offspring either die before or shortly after birth. There is something about hereditary achondroplasia that is lethal to rabbits.

Scots Dumpys look like normal chickens on wee legs.
Scots Dumpys look like normal chickens on wee legs.

Achondroplasia in Chickens

Believe it or not this gene has showed up naturally in one breed of chickens, the Scots Dumpy. This Scottish breed of chicken has had a lot of names over the years including the ever adorable creepies, crawlers, and stumpies. These short and stout chickens are the same size as most large fowl weighing up to seven pounds in adulthood but with the unusual characteristic of standing only two inches off the ground giving them an elongated stout posture.

This breed has an ancestry that goes back at least as far as the 11th century and likely long before then but today it is considered a breed in danger of extinction as it has not maintained popularity and breeders often complain of the same 25% fetal death that occurs before their eggs hatch that I have mentioned in the Munchkin cats. Still many people find the weird waddling gait to be worth a watch.

And achondroplasia can also be induced in chicken embryos in a laboratory setting when scientists inject 0.6 mg of thallium sulfate into each egg between the 5th and 8th day of development. This may give insight into the condition as a whole, especially in cases that are environmentally, not genetically, caused.

Nubian Goat Kid
Nubian Goat Kid

Acondroplasia in Goats

Although there are several breeds of dwarf goats only the Nigerian Dwarf and the African Pygmy show the achondroplasia gene in the United States. These goats are often used for milking or are used as pets but in Africa they are also very commonly eaten as well. It's not clear if these goats were intentionally bred because of their short stature of it they were merely allowed to breed until they reached their current robust population, but either way they have become very common in both Africa and the United States. They may be slightly more prone to obesity than regular goats but it's not clear if this is because of the achondroplasia or just because Americans really love feeding treats to their pets. Who knows!

Dexter Bull
Dexter Bull

Achondroplasia in Cows

Although achondroplasia frequently pops up at random, usually in beef cattle breeds, this trait is usually seen as a defect and culled. The only breed of cattle I could find which encouraged it was the Irish Dexter, a type of miniature cow, which clearly displayed the shortened legs, the broadened skull, and with an unfortunate propensity to birth "bulldog cattle" which were grossly mutated offspring with even shorter legs and often cranial deformities. These calves usually die before adulthood. Curiously although these cows clearly have acondroplasia scientific studies have shown it is not from the same gene mutation as in humans. This opens the possibility that many of the animals listed above may in fact have a series of different gene mutations, not any singular one, that just happens to have the same effect.

Achondroplasia in Horses

Achondroplasia in horses is an interesting concept because it's usually found in already miniaturized breeds but are not the source of the miniaturization. Miniature horses were bred through dozens, perhaps hundreds, of generations to be increasingly small by breeding the smallest mares to the smallest studs that were available. Curiously it was after this that the achondroplasia showed up and stranger still it is not the defining feature of any one breed of miniature horse, instead it shows up in 25-50% of all of the combined breeds. They have shorter upper legs and ears than their peers. They have a higher tendency to be born with contracted legs and loose tendons and can suffer higher rates of arthritis.

Conclusion

Achondroplasia is a very old gene (or series of genes) that has been bred into animals for almost as long. Sometimes this comes at a cost, other times this results in perfectly healthy animals, and it is up to both breeders and the pet owners who buy from them to decide whether or not these are features we want to continue encouraging or not. I hope you found this article fun and informative. If you'd like to read some of my other genetic articles feel free to take a gander. I've listed some below.


Mammal Hybridization: The Truth and The Myths

Why are Calico Cats Always Female?

Miniature Livestock: An Overview

Examples of Insular Dwarfism

The Truth about Tabbies: Basic Tabby Cat Genetics

Genetic Anomalies in Rats

Thirteen Animals You Didn't Know were used in Laboratory Research

The Misunderstood Practice of Culling - What it Really Means


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Comments 7 comments

Peggy W profile image

Peggy W 2 years ago from Houston, Texas

Very interesting hub about a genetic anomaly which causes dwarfism in animals. It certainly flies in the face of nature when purposely bred intentionally by people for specific looks or characteristics. Up, useful and interesting votes.


Theophanes profile image

Theophanes 2 years ago from New England Author

Thank you Peggy W. I am afraid most selective breeding done by humans "flies in the face of nature" but that doesn't always cause problems. This is just one of many things that has a mixed history. Thank you for reading, commenting, and voting!


DrMark1961 profile image

DrMark1961 2 years ago from The Beach of Brazil

Interesting hub, as always. Terrible condition to have, though. Ask any Doxie--this sort of explains their temperament though, right?


Theophanes profile image

Theophanes 2 years ago from New England Author

It could! I haven't been around too many doxies, all I hear is they're near impossible to potty train because you never know when they're squatting... That alone would make me want to avoid the little buggars...

Thanks for stopping by, it's always a pleasure to see you around.


MJennifer profile image

MJennifer 2 years ago from Arizona

Theophanes, this hinges on a subject that I often contemplate. As a long-time horse breeder who has raised many other types of animals, I strive for ethical propagation. One of my own rules for myself is that I will never knowingly breed an animal that may pass along genes that will cause its offspring undue discomfort or misery -- and that includes dwarfism that can cause back subluxations and other ills. That's not to say that I don't appreciate these animals and often find them a joy to be around nor to say that they can't have happy, wonderful and active lives (my Mom's little Doxie has been an outstanding dog and if I could judge by his grinning face and wagging tail, he's certainly happy). It's an interesting topic and certainly worthy of discussion. Well presented!

Best -- MJ


Theophanes profile image

Theophanes 2 years ago from New England Author

Thank you MJ for that well thought out comment. My introduction into the big and strange world of genetics started with breeding fancy rats many many years ago. From there I branched out and like you had my hands in a lot of different critters when I started to see the broader patterns. At one point I had some Munchkins, my stud was furless as well, but this was in the days we just didn't know much about them, they were too new. Sure enough although I had healthy kittens I found my stud dead one day after showing no symptoms of illness whatsoever. Turns out both furless and munchkin breeds have a propensity for heart problems. It was tough thing to learn. Given the same opportunity today I think I'd decline but that's just my view. It's good to at least think about these things. I can certainly appreciate there are others out there pondering these ethical issues too. Thank you for the comformation!


Nell Rose profile image

Nell Rose 2 years ago from England

Fascinating look at the Dwarfism in these animals, I remember another genetic anomaly about bulldogs, their poor little noses can't breath properly because of all the selective breeding, they look cute yes, but I do think its cruel, great read, nell

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