IVDD: Why Short Legs and Bad Backs Come From the Same Gene
The retrogene that gives a Dachshund its short legs is the same one that wrecks its discs. It is not a side effect of the shape, it is the shape, and the odds ratio attached to it is 51.
IVDD: Why Short Legs and Bad Backs Come From the Same Gene
IVDD stands for intervertebral disc disease. To make sense of it you need to know what the disc is.
Think of the spine as a string of pearls: bony vertebrae separated by discs. Each disc has a gel-like center called the nucleus pulposus sitting inside a tough outer ring of fibrous cartilage called the annulus fibrosus. Together they let the spine bend, flex and turn while cushioning the vertebrae against shock. In a young animal the nucleus is up to 88% water.
When a disc degenerates or is damaged it can bulge like a jelly-filled donut, or rupture outright, pressing on the spinal cord or the nerve roots branching off it. The reason this is so serious is anatomical: the spinal cord runs through a tunnel of bone, so displaced disc material has nowhere to go except into the cord.
Lifetime prevalence across all dogs is about 3.5%. Roughly 65% of cases involve the thoracolumbar spine, the back, and about 18% the neck alone.
Two Kinds, and They Are Not the Same Disease
| Hansen Type I | Hansen Type II | |
|---|---|---|
| What happens | Extrusion: the nucleus ruptures through the ring | Protrusion: the ring itself thickens and bulges |
| Underlying change | Chondroid metaplasia, early drying and calcifying | Fibroid metaplasia, slow collagen maturation |
| Onset | Acute, painful, progressive | Slowly progressive, often not painful |
| Typical age | 3 to 6 years, sometimes 1 to 2 | 8 to 10 years |
| Typical breeds | Dachshund, French Bulldog, Beagle, Pekingese | Doberman Pinscher and other large breeds |
In chondrodystrophic breeds the disc degenerates within the first few months of life, and extrusion can happen as early as one to two years of age with acute, severe signs. In large breeds the same tissue matures slowly instead, and problems appear after about five years as gradual wobbliness and weakness.
Worth knowing that this tidy split is being questioned. Recent histopathology finds features of chondroid metaplasia in both breed groups, challenging the traditional Type I versus Type II distinction. There are also newer categories outside Hansen's framework entirely, such as acute non-compressive nucleus pulposus extrusion, which happens during exercise in relatively young dogs with healthy discs.
The Gene That Does Both Things
Chondrodystrophy means altered endochondral ossification producing shortened long bones: the short-legged, long-backed silhouette. Cornell abbreviates it CDDY. In dogs it traces to a retrogene, an extra reinserted copy of a gene, in this case fibroblast growth factor 4.
Dogs carry two FGF4 retrogenes, one on chromosome 18 and one on chromosome 12. The chromosome 12 copy is the consequential one.
| Finding | Figure |
|---|---|
| Odds ratio for IVDD, chromosome 12 retrogene | 51.23 (95% CI 46.69 to 56.20) |
| Inheritance for height | Semidominant |
| Inheritance for disc disease | Dominant |
| FGF4 expression in neonates with two copies | 20 times higher in the disc |
| Surgical cases carrying one or two copies | 75.2% of 569 cases across 61 breeds |
That combination of inheritance patterns is the cruel part. One copy gives only modestly shortened legs, but because the disc effect is dominant, one copy is enough for the full disc risk. A dog does not have to look like a Dachshund to have a Dachshund's spine.
The effect on the disc itself shows up plainly in calcification rates: 84.8% of dogs with two copies had calcified discs, against 63.8% with one copy and 18.5% with none. Dogs carrying the retrogene also came to surgery roughly 27 to 31 months younger than those without.
These mutations are ancient. FGF4 has been retrotransposed twice in dogs within the last three to four thousand years, and there are descriptions of short-legged dogs going back over four thousand years. The genetics of the Dachshund's back predate the breed by millennia.
Carrier frequency is close to fixed in some breeds. For the chromosome 12 retrogene: Beagle 1.00, Dachshund 0.99, French Bulldog 0.94, Pembroke Welsh Corgi 0.92, Basset Hound 0.83. Cornell's affected list also includes Cavalier King Charles Spaniels, Cocker Spaniels, Miniature Poodles and Pekingese.
The Dachshund Numbers
| Measure | Figure |
|---|---|
| Lifetime prevalence, Miniature Dachshund | About 20% |
| Lifetime prevalence, all dogs | About 3.5% |
| Share of all IVDD cases (ACVS estimate) | 40 to 75% |
| Survey prevalence, 2,031 Dachshunds | 15.7% (95% CI 14.1 to 17.3) |
| Highest variety: Standard Smooth-Haired | 24.4% |
| Lowest variety: Standard Wire-Haired | 7.1% |
Disc calcification in Dachshunds peaks between 24 and 27 months of age, which is precisely why the radiographic screening scheme used by breeders images dogs at 24 to 30 months. Dogs scoring 2 or fewer calcified discs are suitable for breeding, 3 to 4 should be bred judiciously, and 5 or more should be excluded.
Severity, and the One Test That Matters
Clinicians grade thoracolumbar injury on the Modified Frankel Scale, six categories from normal to paraplegic without sensation. Be aware that different authors number it in opposite directions, so the descriptions matter more than the numbers.
Deep pain perception, usually written DPP, is the pivotal finding. It is tested by pinching the bone of a toe or the tail and watching for a genuine behavioral response, a bark or a turn of the head. A reflex flexion of the limb must not be mistaken for one. In a paraplegic dog, whether DPP is present is the most important prognostic finding there is.
| Presentation | Recovery after surgery |
|---|---|
| Ambulatory dog, cervical disc disease | 95% |
| Non-ambulatory small breed, back, DPP intact | 85 to 95% |
| Non-ambulatory dog, cervical disc disease | 65 to 95% |
| Small breed, back, DPP lost | 50% |
| Non-ambulatory large breed, chronic protrusion | 25 to 50% |
Speed matters even where the eventual outcome does not. For dogs paraplegic with intact deep pain, mean time to walking again was 15 days after surgery versus 84 days with conservative treatment.
The worst outcome, progressive myelomalacia, is a spreading softening of the cord that develops in 5 to 10% of dogs that are paraplegic with lost deep pain. Affected dogs develop flaccid paralysis that ascends until breathing fails. Delay beyond 12 hours is associated with increased risk, which supports decompressing severely injured dogs within 12 to 24 hours. Notably, there is no evidence supporting the widely repeated 48-hour cutoff beyond which recovery is supposedly impossible.
Treatment
Dogs with pain and mild to moderate deficits often recover with two to three weeks of cage rest. A short course of prednisone can relieve pain, but there is no evidence that steroids or any other drug improves neurological recovery.
One safety point deserves emphasis: giving pain relief without enforcing cage rest is contraindicated, because a comfortable dog moves more and may extrude more disc material. Signs recur after conservative treatment in 30 to 40% of cases.
Surgery is a ventral slot for the neck, or hemilaminectomy for the back. Prophylactic fenestration of commonly affected disc spaces reduces recurrence: one randomized trial of 207 dogs found 7.5% recurrence with multi-site fenestration against 18% with single-site.
What the Evidence Does Not Support
This is the section most articles skip, and it matters more than the rest.
Restricting exercise appears to be backwards. Dachshunds exercising more than an hour a day had reduced odds of IVDD (OR 0.50), while those exercising under 30 minutes had increased odds (OR 2.49). One review concludes plainly that the common clinical recommendation to restrict activity in these breeds "might be counter-productive."
Banning stairs and furniture has no support as prevention. Dogs not allowed on furniture had higher odds, and dogs doing no daily stairs had higher odds than those doing a full flight. This is very likely reverse causation, owners restricting dogs after a diagnosis, so it is not evidence that stairs protect. But it is not evidence for the ban either.
Glucosamine and chondroitin showed higher odds of IVDD, again almost certainly because owners start them after diagnosis. Either way there is no evidence they prevent it.
Routine physiotherapy has not been shown to improve locomotor outcome in mild to moderate cases, across two prospective trials.
Two things that are supported: delaying neutering, particularly in females, where neutered females carried a relative risk of 1.81 and those neutered under 12 months 2.12; and buying from tested parents, since genetic testing for the retrogene exists and breeders can plan matings around it.
The blunt summary from VCA is worth quoting directly: there is no way to prevent intervertebral disc disease.
For the affected breeds covered on this site, see our French Bulldog guide, whose spinal issues sit alongside its airway problems, and our small breed dog guide.
Sources & Further Reading
- Merck Veterinary Manual: Degenerative Diseases of the Spinal Column and Cord
- Cornell Riney Canine Health Center: Chondrodystrophy and IVDD (CDDY/IVDD)
- An FGF4 retrogene on CFA12 is responsible for chondrodystrophy and IVDD
- Phenotypic Effects of FGF4 Retrogenes on Intervertebral Disc Disease in Dogs
- DachsLife 2015: risk factors for IVDD in Dachshunds
- Prognostic factors in canine acute intervertebral disc disease
Also consulted
- Cornell Riney Canine Health Center: Intervertebral Disc Disease
- VCA Animal Hospitals: Cervical Intervertebral Disk Disease in Dogs
- Fenn J et al. "Classification of Intervertebral Disc Disease." Frontiers in Veterinary Science, 2020.
- Dorn M et al. "Neuter status as a risk factor for canine intervertebral disc herniation (IVDH) in dachshunds: a retrospective cohort study." Canine Genetics and Epidemiology, 2018.
- Rosenblatt AJ et al. "Scorer and modality agreement for the detection of intervertebral disc calcification in Dachshunds." Acta Veterinaria Scandinavica, 2018.
- Current approaches to the management of acute thoracolumbar disc extrusion
❓ Frequently Asked Questions
What does IVDD stand for?
Intervertebral disc disease. An intervertebral disc is the cushion between two vertebrae, with a gel-like core called the nucleus pulposus inside a tough fibrous ring called the annulus fibrosus. The discs let the spine bend and absorb shock. When one degenerates it can bulge or rupture into the spinal canal, and because the cord runs through a tunnel of bone there is nowhere for that material to go except into the cord.
How common is IVDD in Dachshunds?
Miniature Dachshunds have a lifetime prevalence of around 20%, against roughly 3.5% for dogs overall. A survey of 2,031 Dachshunds found 15.7% affected, and it varied by variety: Standard Smooth-Haired highest at 24.4%, Standard Wire-Haired lowest at 7.1%. The American College of Veterinary Surgeons estimates Dachshunds alone account for 40 to 75% of all IVDD cases.
What is the FGF4 retrogene?
An extra, reinserted copy of the fibroblast growth factor 4 gene. Dogs carry two, one on chromosome 18 and one on chromosome 12. The chromosome 12 copy produces both the short-legged build and premature disc degeneration, with an odds ratio of 51.23 for IVDD. It is semidominant for height but dominant for disc disease, so one copy is enough to carry the disc risk.
What is deep pain perception and why does everyone ask about it?
It is the deepest level of sensation in the limbs, tested by pinching the bone of a toe or the tail and watching for a real behavioral response such as a bark or turning the head. A reflex twitch of the leg does not count. In a paralyzed dog it is the single most important prognostic finding: with it intact, surgical recovery runs 85 to 95%, without it around 50%.
Do stairs and furniture cause IVDD?
The evidence does not support the usual advice. In a survey of 2,031 Dachshunds, dogs not allowed to jump on furniture had higher odds of IVDD, not lower, and dogs doing no stairs daily had higher odds than dogs doing a full flight. That is almost certainly reverse causation, owners restricting dogs after a diagnosis. What it does mean is that banning stairs has never been shown to prevent anything.
Written by Mike
Mike is the founder of Beastly Facts and a lifelong reptile enthusiast. He shares his home with Dex, a bearded dragon with strong opinions about crickets and basking schedules. Mike writes in-depth care guides, animal facts, and the occasional short story about life with exotic pets.
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