A Research Study · Open Call for Participants
The Proportionate Dwarfism Study
Conducted by Rev. Tanya Stringer, M.Div, FGC
Across the Chihuahua community, a single line on an Embark report — "At Risk for Proportionate Dwarfism" — is causing breeders to remove perfectly healthy dogs from their programs and pet owners to fear a disease their dog has never shown. This study asks a simple question: does the test actually identify a disease at all?
Embark's Proportionate Dwarfism test is built on one published paper, describing one dog — a 2020 case report of a single Chihuahua puppy with growth hormone deficiency. In the five years since publication, no second case has been reported in the scientific literature. No follow-up study has confirmed the variant causes the disease. No functional test has been performed. The test moved from one case report into commercial breeder panels with nothing in between.
This study is the missing middle.
Section 01
The findings so far
Of 113 Chihuahuas tracked in this program, 41 have been tested by Embark for the GH1 c.573_578del variant.
22
Clear
17
Carrier
2
At Risk (homozygous)
The two "At Risk" dogs — Andy and Sugarbaby — come from two independent kennels. Both carry two copies of the variant. According to the original 2020 paper, dogs in this category should be unmistakably affected: severely underweight, collapsing from low blood sugar, with retained baby teeth and an undeveloped puppy coat at six months of age.
What we found instead:
Both homozygous "At Risk" dogs are phenotypically normal, healthy adult Chihuahuas. Neither shows a single clinical sign described in the original paper.
How they compare
| Clinical Sign | 2020 Case Report | Our At Risk Dogs |
|---|---|---|
| Body weight | 1.94 lb at 6 mo | 5–6 lb adult |
| Hypoglycemia | Severe, recurrent | None |
| Open fontanelle | Open | Closed / tiny |
| Retained baby teeth | Yes | None |
| Puppy coat retention | Yes | Normal adult coat |
| General health | Failed GH testing; collapse | Passed all health testing |
In addition, when adult body weights of every tested dog in the program were compared by genotype, there was no statistically significant difference between Clear, Carrier, and At Risk dogs (Kruskal–Wallis p = 0.698). The smallest dog in the entire tested cohort was a Clear dog. Both At Risk dogs are larger than the smallest Clear dog.
Full Scientific Review
Critique of Iio et al. (2020) and Empirical Case Series
A formal critique applying ACMG/AMP 2015 variant interpretation standards to GH1 c.573_578del, including the empirical case series presented above.
Section 02
How to participate
If your Chihuahua was tested by Embark — for any Proportionate Dwarfism result — you can contribute. Clear, Carrier, and At Risk dogs are all needed; this is a population study, not just a search for affected dogs.
- 1
Send your dog's full Embark PDF
Download the complete report from your Embark account and email or message it. The summary page contains the Embark swab/kit ID, which is the dog's identifier in the study. You do not need to share the registered name.
- 2
Tell us about your dog
A short description is enough. The information that matters most:
- Adult weight (in pounds or kilograms)
- Molera / fontanelle — open, closed, or tiny?
- Did any baby teeth fail to fall out on their own?
- Any low-blood-sugar episodes as a puppy?
- Any health issues at any age?
- Current age
- If you have IGF-1 bloodwork, that is gold — please include it. Not required.
- 3
Give permission to use the information
A simple "yes, you may use this in your published study" in your email is sufficient. The dog will be identified only by Embark swab ID and call name. Your name and kennel name will not be used unless you specifically tell us we can.
Privacy
The Embark swab ID is enough to identify a dog scientifically. Registered names, microchips, and owner information are not required for the study. Owners and kennels are credited in the acknowledgments section of any publication only with explicit permission.
Pet owners and breeders are equally welcome. Show dogs and pet dogs count the same. Any country, any age. The more diverse the cohort, the stronger the evidence.
If you'd like to be included on a list for future Chihuahua health studies, just say so when you write. We're working on more.
Section 03
Why this matters
Genetic testing has been transformative for purebred dog health. The validated tests on Embark's panel — for medication sensitivity, retinal degeneration, intervertebral disc disease, the size genes, and many more — have prevented real suffering and helped breeders make better decisions. None of that is in question here.
What is in question is what happens when a single case report becomes a commercial test result before the science has caught up. A breeder removes a dog from her program. A pet owner panics about a disease their dog has never shown and never will. A puppy buyer rejects a litter. Meanwhile, the test result is grounded in evidence that, by accepted standards in human medical genetics, would be classified as a "Variant of Uncertain Significance" — not as a cause of disease.
This study exists to put real evidence next to a result that currently has very little behind it. If the variant is pathogenic, more cases will surface. If it isn't, the data will show that too. Either outcome serves the breed.
Section 04
About this study
This research is conducted by Rev. Tanya Stringer, M.Div, FGC — a Forensic Genealogist Credentialed whose professional work involves applying rigorous standards of genetic and documentary evidence in legal and regulatory contexts. She is the medical author for Chi Chatter, the national magazine of the Chihuahua Club of America.
Findings from this study are being prepared for submission to a peer-reviewed veterinary genetics journal.
Section 05
With thanks
In Recognition
Rebecca Giacobbi
Pawsitive Cheeky Chihuahuas
For going above and beyond for the breed. An outstanding breeder whose generosity, transparency, and willingness to share data made this study possible. The Chihuahua community is better for breeders like Rebecca.
Thanks are also owed to every breeder and owner who has responded to the recruitment call. Each dog you contribute makes the next step in this work stronger.