There are three common and valued genetic conditions in dogs that result in stunted growth: pituitary (ateliotic) dwarfism which results in proportional minis, micromelic achondroplasia which results in shortened limbs, and brachycephalic achondroplasia which shortens the head.
All of these conditions are genetic disorders and all of them are definitive sine-qua-non features of some breeds, often in combination. These disorders aren’t accidental and unwanted, they are written into the breed standards. The breed wardens don’t want to breed these conditions out, they demand they breed true.
Mix and match your genetic dwarfism disorders.
Most of the toy breeds are ateliotic dwarfs: Chihuahuas, Boston Terriers, Italian Greyhounds, Maltese, Miniature Pinschers, Miniature Spaniels, Pomeranians, Toy Poodles, Yorkies, etc. This form of dwarfism is caused by a deficiency in somatropin which results in stunted growth of all somatic cells in the body. Ateliosis is a recessive allele.
If you’re a self-styled expert with a bad case of illusory superiority who has written more books than he’s read, you might say, “‘Achondroplasia’ literally means ‘an absence of good shape,’” but that’s not what the literal Greek means. “Chondro” is Greek for cartilage and “Plasia” means growth or change from the Greek word for moulding. Thus, the literal meaning of Achondroplasia is “Defective growth of cartilage” and that’s pretty much what it is. In general, it serves as the name for a cluster of similar disorders of the cartilage and bone (osteochondrodysplasias).
The most obvious effects of Achondroplasia occur in the long bones of the leg and “micromelic” means short limbs. Micromelic breeds include: Basset Hounds, Bulldogs, Corgis, Dachshunds, Lhasa Apsos, Scottish Terriers, Shetland Sheepdogs, etc. Micromelic Achondroplasia is a dominant allele with incomplete penetrance.
Another form of Achondroplasia that doesn’t lead to what we commonly consider to be dwarfism but which likewise results in insufficient growth of bone is Brachycephalic Achondroplasia which shortens bones in the skull. In dogs, shortening of the mid-face and maxilla and shortening of the lower jaw are inherited separately. Boxers have a shortened upper jaw, but their lower jaw is normal and they are normal sized in all other respects; whereas Boston Terriers have both upper and lower brachycephalism and are also ateliotic dwarfs, so they are proportional but small with smooshed faces.
Bulldogs have midface and upperjaw brachycephaly so their lower jaw juts out and they have trouble breathing, and they also have micromelic achondroplasia so their legs are short and bowed while their trunk is not significantly
Miniature Dachshunds carry both forms of body dwarfism, but their faces are unaffected.
And what do you get when you combine all three disorders? A Pug.
The most completely achondroplastic dog breeds are the toy imports of East Asia origin (bracycephalic + micromelic achondroplastic + ateliotic): the Pekingese, the Shih Tzu, and the Pug. The body-forms of these triply achondroplastic breeds represent the simultaneous superposition of all three varities of achondroplasia–micromelic, maxillary, and mandibular–on a midget frame. Thus, the Pug’s disproportionately stumpy legs, tending to bow (genu varum), result from micromelic achondroplasia. The Pug’s bulging forehead (frontal bossing); large, staring eyes (exophthalmos); pronounced stop (recessed nasion); and short midface (midface hypoplasia) all reflect maxillary achondroplasia. The Pug’s short lower jaw expresses mandibular achondroplasia. The Pug’s extraordinarily flat face and crowded dentition are accidence of the simultaneous operation of maxillary and mandibular achondroplasia.
- For the Love of Dachshunds, Robert Hutchinson
None of these disorders exist without other health complications like luxating patellas, arthritis, cataracts, and shortened lifespans. But, none of these disorders can be removed from breeds without fundamentally altering the breed itself. The Miniature Dachshund would simply be a Dachshund if you removed the pituitary dwarfism, but most of the other dogs no longer have a perfect corresponding wildtype breed.
For that reason, if the disease is to go, the breed is to go. I won’t count on that happening any time soon, if ever.
Diseased Dwarf Dog images provided courtesy of Cartoonize My Pet.
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Nora
Jess
Pam
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Lori Ziemba
I suppose I wouldn’t be so biased against the dwarfed breeds if they didn’t do two things:
a) Breed for the obviously major dysfunctions.
Once you see a dog that can’t walk, only waddle or a dog that can’t breathe – it’s hard to imagine how these are “desirable traits”.
b) Breed so selectively for certain traits like “teacup size” dogs that you are certain to hear the phrase “normal for the breed” for various problems that are practically unheard of in other breeds.
I’m beginning to think “normal for the breed” is one of the most terrifying phrases one can hear. It implies that what would otherwise be a “known problem” that ethical breeders try to minimize in their animals has become accepted as “normal”.
Very interesting info. I own Pomeranians which seem to be similar to the Dachshund example. If they “grow” larger, they are then considered to be Klein or Mittelspitz. In FCI countries, it is one breed with various divisions i.e, Zwergspitz (Poms) Kleinspitz (what we call “Victorian” Poms), Mittelspitz, Wolfspitz (keeshonds) and Giant Spitz.
I had also read that there was a genetic cause for small size in some cases, which did not include a defect in somatropin (otherwise known as Growth hormone)
There is a widespread defect in Pomeranians called “Alopecia X” which is, curiously enough, also a defect that may be associated with growth hormone deficiency and dwarfism. However, Growth hormone administration has not proven helpful for this condition. There is a search currently for the cause of alopecia X in Pomeranians. It is presumed to be a genetic defect. Time will tell, I suppose.
Thanks for the info Geneva. So far, the book I link to in this post is the only good source I have on “ateliotic dwarfism” … so far it’s a very nebulous condition. One might say that it can simply be bred down to. Others might say it’s a disorder or disease. I am satisfied in saying that it’s really up in the air but it’s better to err on the side of appreciating that there might be negative side effects and while it might not be a simple single gene “disease” … we should, as you suggest, keep an eye on it. This might be a tandem repeat situation where we can get very fine gradients in phenotype, or it might be different alleles of a single gene locus.
The toys are well established and some are ancient. They’ll get by with pituitary dwarfism as they have, but the more we know about it the more we can prevent the real issues like when they start combining really really short noses and cork tails… I mean, the Pug is a mess.
when your adverts for show puppies make people throw up you really need to rethink your breeding program http://forums.moneysavingexpert.com/showthread.php?p=51712631
maybe instead of vets and judges at crufts we should ask a random member on the non dog owning public their opinions.
Odd-looking puppies. But I’ve never seen an English Toy spaniel at that age (or King Charles spaniel, which is the UK name).
I agree with the second response on that thread: why is the breeder advertising on a site for rehoming dogs, and why are the puppies shy? That’s more bothersome than the odd-shaped heads (then again, as a collie person my perception of “odd-shaped heads” is probably a little skewed).
I’m a little curious: how short can a dog’s snout or legs be without being dwarfed? And is it possible to breed toy-sized dogs without dwarfism coming into play?
Yes. IGs, Minpins, Papillons, Toy Manchester terriers, Toy Rat terriers, none of these are dwarfed dogs.
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It’s my understanding that those dogs would be considered pituitary dwarfs.
The pituitary is the gland that produces several main growth hormones and there are ostensibly two ways you can use this to alter the same of dogs, one being natural variation in pituitary production and the other being diseases such as tumors that effect the pituitary in radical ways.
It is likely that if you breed for small dogs over many generations you will find that you have selected for reduced pituitary output.
In some breeds we see radical inherited pituitary dysfunction that results in dwarf dogs that are not likely to survive for very long (i.e. GSDs).
Pituitary selected dwarf dogs are more likely to be proportional and to my knowledge they are not known to have the same degree of associated problems (but they are not free from problems, there are issues with being small!).
Yes I know something about the Pituitary gland as i have a growth on mine & it affects things like sexual maturity, hormounes & that in it’s self can lead to a host of secondary symtoms. It also has a lot to do with height, I’m taller than the magority of females but it can go the other way & make you to short too it depends on how the gland is affected.
I’m not sure where you get that Shelties are micromelic? Coat length sometimes makes it LOOK that way, but if you put hands on the dogs (or wet them down) they tend to be nearly square (back just a little longer than legs) and quite proportional. There was a fashion some years ago for what many of us derisively called “shorgis” (longer-backed, shorter legged dogs), some of which MAY have been micromelic, but you don’t see that in either the show or performance dogs now.
The show dogs’ legs are heavily chalked and fluffed to make it look like they have “lots of bone” (despite a standard that calls for moderation) but in general, in an unfluffed state they are very moderate. Most of the Shelties I see who REALLY have “lots of bone” are also oversized by breed standard.
The source is linked in the article:
For The Love of Dachshunds, by Robert Hutchinson
The link is to the book on google.com. I searched within the book, and there is no mention of Shetland Sheepdogs and micromelic (though there are references to other dwarfed and micromelic breeds).
Are you sure, that pug has an ateliotic dwarfism? How it can be noticed if it’s brachycephalia is so serve, that it masks all visible signs of A. dwarfism?
Just wanted to mention that bulldogs are not micromelic. They have normal shaped, untwisted limbs. They may look twisted because of the bench front which puts them out at the elbows, but the limbs are straight. Pugs also have normal limbs.