Chip
MRI-cleared control · Australia
CM 0 / SM 0
A 4 lb Chihuahua imaged in Australia with a clear MRI. Structurally favorable across every metric. Confirms the model predicts non-affected status correctly.
The Research Program
N° 02 Neurology · Structure · Lineage
Research
The CM/SM Risk Lineage Study
A breeder-led research program tracing the structural and lineage roots of Chiari-like Malformation and Syringomyelia in the Chihuahua — and giving breeders, owners, and veterinarians the tools to screen for it.
— Rev. Tanya Stringer, FGC, M.Div. · Lead Researcher
The Study
What we are doing — and why it matters
Chiari-like Malformation (CM) and Syringomyelia (SM) are no longer concerns confined to the Cavalier King Charles Spaniel. Published work by Kiviranta et al. (2017) and Knowler et al. (2017) found CM in essentially every Chihuahua imaged, with SM in roughly 38% of cases. Clinical neurologists I have spoken with at Cornell, Upstate Veterinary Specialties, and Elemental Pet Vets agree: 30–50% of Chihuahuas would show SM if universally MRI-screened.
Despite that, no structural-screening protocol exists for the breed. The CM/SM Risk Lineage Study was built to change that — from inside the breeder community, using tools breeders can actually use.
What makes this study different
- Breeder-led and proactive. Most CM/SM research follows symptomatic dogs into the clinic. This one starts with the population before symptoms appear.
- Structural + genetic + lineage. Head and neck morphometry, BMP3 and IGF1R1 genotypes, and forensic-genealogy tracing are integrated into one risk model.
- Calibrated against known cases. Scoring thresholds are validated against an MRI-cleared control, an MRI-confirmed SM case, and a necropsy-confirmed severe CM case.
- Free and open to participants. Including a free forensic-genealogy lineage analysis on every submitted pedigree.
We cannot breed CM out of the Chihuahua — the apple dome that defines our breed is also the structural feature that creates it. But we can reduce SM by avoiding the structural extremes: very wide skulls, very short skull bases, and very short necks.
Working Findings
What 38 measured Chihuahuas are telling us
These figures reflect the current working dataset and update as new participants join. They are working observations, not final published statistics.
79%
Carry at least one CM flag
18%
Meet High CM Risk
14%
Meet High SM Risk
21%
Score structurally clean
The two strongest structural signals
For CM: a wide skull paired with a short skull base. Width of head 7.0 cm or more combined with an Occiput-to-Stop length of 5.0 cm or less is the single worst combination in the dataset. This is the geometry behind a brain with nowhere to sit.
For SM: neck length. Spinal fluid has to flow freely from the brain through the cervical spine. Our MRI-confirmed SM Grade 2 case had a 7.0 cm neck. We treat 8.0 cm or less as a warning, with stronger signal in the Neck-to-Head ratio — 0.85 or below indicates a relatively short neck for the dog's head size.
The simple score-card thresholds
| Measurement | Favorable | Warning |
|---|---|---|
| Width of head | < 6.0 cm | ≥ 7.0 cm |
| Skull base (Occ–Stop) | ≥ 6.0 cm | ≤ 5.0 cm |
| Muzzle (Stop–Nose) | ≥ 2.5 cm | < 2.0 cm |
| Neck length | > 8.5 cm | ≤ 8.0 cm |
Three or more measurements in the warning column places a dog at High CM Risk. The veterinary worksheet uses an 8-flag system that adds the cervical ratios for SM stratification.
Calibrated against known cases
Brinley
MRI-confirmed SM Grade 2 · symptomatic
CM 3 / SM 5
The study's foundational case. Both CM and SM scoring register as High, matching the imaging and the dog's clinical presentation.
Butters
Severe CM confirmed at necropsy · asymptomatic in life
CM 3 / SM —
An Occiput-Stop of 4.0 cm — the shortest in the dataset. Lived without clinical signs. Validates that severe CM exists undetected and that structural screening matters even for asymptomatic dogs.
Lineage Finding
One name, every confirmed case
Forensic-genealogy tracing across every confirmed CM/SM case in the study has produced a single recurring ancestor — an American champion sire born in 1968 whose structural type appears to have anchored a popular-sire bottleneck still echoing through pedigrees today.
This is not a finger pointed at one dog. It is a pattern that helps explain why a structural-risk profile has propagated through so many lines, and why measurement-based screening alone is insufficient without lineage context.
If you submit your dog's pedigree to the study, you will receive a free forensic-genealogy analysis showing how this ancestor — and other recurring problem ancestors we have flagged — appear across 6 to 11 generations of your dog's line.
The Tool
The Breeder Measurement Guide
A free, no-math screening guide designed for breeders and owners to use at home with a soft cloth tape measure. The structural foundation of the study — and the same protocol used to score every dog in the dataset.
How to Measure Your Chihuahua
PDF · A Breeder’s Guide to CM/SM Structural Screening
Walks through seven head and neck measurements with a flexible cloth tape, explains in plain language why each one matters for CM and SM, and translates the results into Low / Moderate / High structural risk bands. No math required.
- Why each measurement matters — written for breeders, not specialists
- Step-by-step landmarks for all 7 measurements
- The Simple Score Card — green / caution / warning zones
- Quick Width-to-Skull-Base and Neck-to-Head lookup tables
- CM/SM symptom checklist — pain, scratching, gait, posture, neuro
- MRI-priority guidance based on your dog’s structural score
- How to share your data and pedigree with the study
Participate
Add your dog to the study
Participation is voluntary, confidential, and free. Because this is a lineage study, participating dogs must be purebred Chihuahuas with a verifiable pedigree — whether they’re a champion in the ring, a retired show dog, or a beloved companion at home.
Eligibility
- Purebred Chihuahuas — long coat or smooth, any color
- Registered with AKC, UKC, CKC, an FCI member registry, or equivalent — with a pedigree of at least 5 generations available
- At least 12 months old at the time of measurement
Dogs without a pedigree cannot be entered into the lineage analysis, but their measurements and clinical history are still welcomed for the structural reference dataset.
Submit
Worksheet · Photos · Pedigree
Lateral and dorsal head photos, plus a 5- to 7-generation pedigree (required for lineage entry).
Where science meets the soul of the Chihuahua.
© 2026 Alfheim-Andromeda Chihuahuas · CM/SM Risk Lineage Study · v1.0
Rev. Tanya Stringer, FGC, M.Div. · Lead Researcher