Alfheim-Andromeda Chihuahuas
The Research Program
N° 04 Health · Genetics · Longitudinal

Open Evidence-Gathering Study · ATP7B · Est. October 2024

The Chihuahua ATP7B Variant Study

A long-term, primary-source study tracking the ATP7B variant (the gene linked to copper toxicosis in several other breeds) in the Chihuahua. Whether the variant has the same clinical effect in our breed is genuinely unknown. We are gathering evidence, one verified Embark report at a time.

Variant Studied
ATP7B
Study Type
Longitudinal
Submission
Embark + Liver Panel
Status
Open · Accepting

The open question

A variant in the breed. An unanswered question about what it means.

Embark added a Copper Toxicosis (Accumulating) panel to its standard health screen in late October 2024. The panel tests for a variant in the ATP7B gene. In several other breeds, most notably the Bedlington Terrier and Labrador Retriever, this variant has been linked to copper accumulation in the liver and to clinical liver disease. In the Chihuahua, that link has not been established. It may exist. It may not. That is the question this study exists to answer.

When a Chihuahua's Embark report comes back showing one or two copies of the ATP7B variant, the report flags the result as "Notable." Notable does not mean diagnosed. It does not mean affected. It does not mean the dog is sick or will become sick. It means the dog carries a variant that has clinical relevance in some breeds, and that the breed-specific implications are still being worked out.

For the Chihuahua, those breed-specific implications have not been studied. There is no published frequency data for ATP7B in the breed. There is no published clinical correlation study. There is, at present, no evidence that any Chihuahua has developed copper-related liver disease as a result of this specific variant.

"We are not announcing a disease. We are documenting a question. Carefully, transparently, and with primary-source verification."

That is exactly why this study matters. Until the data exists, the question cannot be answered. And until the question is answered, neither we nor the broader breeding community can responsibly say what, if anything, should change about how Chihuahuas are bred, fed, or screened.

What we know

The variant exists.

Embark tests the canine ATP7B gene as part of its standard health screen. Among the Chihuahuas in our archive who have been tested since October 2024, the variant is present at notable frequency.

What we don't know

What it means in this breed.

Whether two copies of the ATP7B variant cause clinical copper accumulation in the Chihuahua. Whether the variant has different penetrance in toy breeds than in larger breeds. Whether age, diet, or other genetic modifiers change the picture. None of these questions has been studied in the Chihuahua specifically.

What we are doing

Gathering verified data.

Logging every Embark report we can verify. Recording the genotype. Asking owners about their dogs' health history: current bloodwork, any liver enzyme history, any clinical signs. Building the dataset that does not yet exist.

Two pathways. One outcome.

Copper accumulation in dogs is not always genetic.

Veterinary medicine recognizes two distinct pathways to copper-related liver disease in dogs. They can look clinically similar (elevated liver enzymes, eventual liver damage) but they have different causes, different progressions, and different implications for diagnosis. Any honest study of a copper-related variant has to grapple with the difference between the two, because conflating them produces conclusions that are not actually supported by the evidence.

Pathway 01

Primary (Genetic)

Caused by an inherited defect in copper metabolism. The body cannot properly excrete copper through bile, and copper accumulates in the liver over a lifetime.

Cause
Inherited mutation in a copper-metabolism gene. ATP7B in Labrador Retrievers and Doberman Pinschers; COMMD1 in Bedlington Terriers; suspected heritable cause in West Highland White Terriers, Dalmatians, and Skye Terriers.
Mechanism
Lifelong, progressive accumulation of copper in liver cells. Copper that should be packaged into bile and excreted is instead retained.
On biopsy
Copper accumulates in a centrilobular pattern (zone 3 of the liver lobule), typically at concentrations exceeding 1000 ppm.
What we test
This is the pathway the ATP7B variant is associated with, but only in breeds where the gene has been clinically linked to disease. The Chihuahua is not one of those breeds.

Pathway 02

Secondary (Environmental)

Caused by excessive dietary copper intake or chronic liver disease that disrupts bile flow. Genetics may not be involved at all.

Cause
Excessive copper in the diet, or any chronic cholestatic or inflammatory liver condition that prevents normal copper excretion. No genetic mutation required.
Why now
Since AAFCO updated its recommendations in 1997 to require more bioavailable copper compounds (such as copper sulfate) in commercial dog food, hepatic copper concentrations have risen dramatically across many breeds.
On biopsy
Copper accumulates in a periportal pattern, distinct from the centrilobular pattern of primary disease. This distribution is the key histologic clue that the cause is environmental, not genetic.
Spreading
Copper-associated hepatopathy is now reported in many breeds without identified genetic mutations, including German Shepherds and Cocker Spaniels, strongly suggesting environmental factors are driving cases independent of inherited variants.

Why this distinction matters for our study

Even a Chihuahua with copper-related liver findings cannot automatically be classified as a victim of the ATP7B variant.

The two pathways look similar at the surface and require histologic analysis (biopsy with copper distribution patterns and quantitative copper measurements) to tell apart. A Chihuahua presenting with elevated liver enzymes or evidence of copper accumulation might be showing primary genetic disease driven by ATP7B. It might equally be showing secondary accumulation driven by a copper-rich commercial diet, just like the increasing number of cases now appearing in breeds without any identified genetic predisposition.

This is part of why the study is deliberately observational and long-term. To draw any honest conclusion about whether the ATP7B variant causes clinical disease in the Chihuahua, we need not only the genetic test result, but also, when available, the dog's diet history, liver bloodwork, and any biopsy findings. Anything less risks attributing to genetics what may actually be coming from the food bowl.

It is also why this study is not, and will never be, a substitute for veterinary diagnosis. If a Chihuahua develops symptoms of liver disease, the cause must be worked out by a veterinarian using the full diagnostic toolkit, not assumed from a single line on a DNA report.

How the variant is inherited

A simple genetic pattern. An open clinical question.

The ATP7B variant follows an autosomal recessive inheritance pattern, the same way it does in any breed where it has been studied. The genetics are well understood. What is not understood is whether two copies of the variant produce clinical disease in the Chihuahua. That is the part this study is designed to investigate.

N / N

Clear

Two normal copies. Does not carry the variant. Cannot pass it to offspring.

N / m

Carrier

One normal copy, one variant copy. Heterozygous. Passes the variant to roughly half of any offspring.

m / m

Two Copies

Homozygous for the variant. In some other breeds this confers risk for copper accumulation; in the Chihuahua, the clinical implication is genuinely unknown.

What we have observed so far

Two findings. Both preliminary. Both worth reporting.

After eighteen months of data collection from October 2024, two patterns have emerged in the dataset. They are based on a small, rigorously verified sample of 24 dogs. They should be read as observations from an early-phase study, not as conclusions about the breed as a whole.

Observation 01 · Variant frequency

Two out of three tested Chihuahuas carry at least one copy of the ATP7B variant.

Among the 24 dogs in our archive who received an ATP7B result on their Embark panel between October 2024 and April 2026, sixteen percent are homozygous for the variant, fifty percent are heterozygous carriers, and one third are clear. The variant allele frequency is 41.7 percent.

16.7%

Two Copies

50%

Carriers · 1 copy

33.3%

Clear · 0 copies

n = 24 · variant allele freq. 41.7% · sample compiled April 2026

Twenty-four dogs is a starting point. It is not a frequency claim about the entire breed and we will not pretend otherwise. But the sample is rigorously verified (every dog has a confirmed Embark test number and a primary-source PDF on file) and the pattern is consistent enough across the small sample to be worth tracking carefully.

Observation 02 · Clinical signs

So far, not one tested dog has shown clinical symptoms of copper toxicosis.

This is the observation that matters most, and it is the one we want to be most careful about. Of every Chihuahua in this dataset, including the four homozygous dogs and the twelve carriers, none has shown the clinical signs typically associated with copper accumulation in other breeds. No reported jaundice. No reported chronic liver disease. No clinical liver failure. No copper-related illness.

That observation can mean several different things, and at this stage of the study we cannot rule any of them out. It may mean the variant has reduced penetrance in the Chihuahua compared to other breeds. It may mean the dogs are too young for the disease to have manifested. It may mean we need a larger sample, longer follow-up, or more detailed bloodwork to detect subclinical changes. It may mean the variant is genuinely benign in this breed. We do not know yet.

What we can say is this: the absence of clinical signs across an entire small dataset is itself a piece of evidence. It is the reason we are not recommending any change in how owners or breeders manage their dogs based on an ATP7B result alone. It is also the reason we want to keep gathering data, because the question deserves a real answer, not a guess.

Tested
24 Chihuahuas in our archive who received an ATP7B result on their Embark health panel between October 2024 and April 2026.
Two-copy
4 Homozygous for the variant. Flagged "Notable" by Embark. None has shown clinical signs of liver disease in our records.
Carriers
12 Heterozygous. One copy. Clinically healthy. Capable of passing the variant to roughly half of any offspring.
Symptomatic
0 No tested dog in this dataset has presented with clinical symptoms of copper toxicosis. This is itself a finding worth recording.

A note on breeding decisions

Removing dogs from breeding programs based on this variant is not recommended.

This is the most important practical statement we can make at this stage of the study, and we want it stated clearly. Given the current state of evidence (the variant's clinical effect in Chihuahuas is unproven, and no tested dog in our dataset has shown symptoms), eliminating dogs from breeding programs based on ATP7B status alone would do measurable, likely permanent harm to the breed's gene pool, in exchange for an unproven and possibly nonexistent benefit.

The math of unintended harm

Eliminate every dog with at least one copy, and you remove two-thirds of the breeding population.

The Chihuahua's gene pool is already smaller than most people realize: toy breeds historically descend from a narrow founding base. Removing two-thirds of that population, in a single generation, based on a variant whose clinical relevance to this breed has not been established, is exactly the kind of well-intentioned reaction that causes new genetic problems faster than it solves any.

50%

Carriers · 1 copy

+ 16.7%

Two-Copy Dogs

= 66.7%

Removed if eliminated

What is lost when two-thirds of a small gene pool is suddenly removed is not just dogs. It is unrelated bloodlines, structural diversity, conformation lines, working temperaments, longevity genes, and resistance to other conditions we may not yet have identified. That kind of diversity loss is documented in other breeds, it is irreversible, and it has measurable downstream consequences.

"In genetics, the cure can be worse than the disease, particularly when we are not yet sure there is a disease."

The responsible path through any autosomal recessive variant, once status is known, is not elimination. It is informed pairing. Carriers can be safely bred to clear dogs and produce no homozygous offspring. Even two-copy dogs can be bred to clear partners and produce only heterozygous carriers. Frequency in the breed can be gradually reduced over generations, without removing a single dog from the gene pool, and without sacrificing the diversity that took decades to build.

What we encourage

Test. Disclose. Plan pairings with full information.

Knowing your dogs' ATP7B status (clear, carrier, or two-copy) is genuinely useful information regardless of what the science eventually shows. Disclose results between breeders and to puppy buyers. Use the information to make pairing decisions you are comfortable with.

What works genetically

Carrier × clear pairings produce no homozygous offspring.

This is standard autosomal-recessive math. A carrier bred to a clear dog produces approximately half clear and half carrier puppies, and zero homozygous puppies. A two-copy dog bred to a clear dog produces all-carrier offspring. Both of these are fully manageable pairings.

What we discourage

Reactive culling without evidence.

Removing carriers and two-copy dogs from breeding programs based on a variant whose clinical effect in Chihuahuas has not been demonstrated will reduce genetic diversity dramatically and likely permanently. The breed cannot afford that loss to chase an unproven risk.

Why this is a long study

An unanswered question takes real time to answer.

If the link between the ATP7B variant and clinical disease in the Chihuahua exists at all, it will only become visible across hundreds of dogs followed over years. A short study cannot answer this question. A small study cannot answer this question. The only honest path is to keep collecting verified reports, keep recording health histories, and keep publishing what we observe, for as long as it takes.

  1. Oct 2024

    Panel added

    Embark adds the Copper Toxicosis (Accumulating) panel to its standard health screen. The first Chihuahua in our archive with an ATP7B result is tested October 8, 2024.

  2. 2024–2025

    Dataset opened

    We begin extracting ATP7B results from every new Embark report in our kennel archive and partner-kennel submissions. The first frequency patterns emerge.

  3. April 2026

    First public summary

    Initial dataset of 24 verified dogs compiled. Frequency observation and absence-of-symptoms observation reported. Public call for additional reports launched.

  4. 2026–2028

    Sample scaling

    Open enrollment continues. Goal: 200+ verified dogs across multiple countries, each with an Embark report and at least one liver panel on file. Participants asked to submit follow-up liver panels every 1–2 years to enable longitudinal analysis.

  5. Ongoing

    Long-term follow-up

    The study is designed as a long-term registry. The repeated liver panels submitted by participants are what make it possible to detect subtle changes in liver values over time, the kind of evidence that could either confirm or rule out a clinical effect of the variant in this breed.

  6. Future

    Honest reporting

    When the data justifies a conclusion, we will publish it. If the data shows the variant is clinically meaningful in Chihuahuas, we will say so. If the data shows it is not, we will say that too. The outcome is not predetermined.

Who we are looking for

Every verified Chihuahua report helps answer the question.

Clear dogs

Yes, we want clear results too.

A frequency study is only as good as its denominator. If you only submit dogs that came back as carriers or homozygous, the dataset becomes biased. Clear results are just as important: they tell us how common the variant isn't.

Carriers

Especially helpful with health history.

Carrier dogs are clinically healthy in every breed where ATP7B has been studied. Confirming this in the Chihuahua is part of the work. If you have any liver bloodwork on file from routine vet visits, we welcome those notes alongside the Embark report.

Two-copy dogs

The most important data we can collect.

Whether or not your homozygous Chihuahua has any clinical signs, your dog's report is critical to this study. A two-copy dog with normal liver values is just as informative as a two-copy dog with abnormal values, possibly more so. We are looking for the truth, whichever direction it points.

How to participate

An Embark report + a liver panel + a follow-up every 1–2 years.

For this study to actually answer the question it asks, we need more than just a one-time DNA result. The genetic test tells us what variant a dog carries; the liver panel tells us whether anything is happening clinically; and the follow-up panels over time tell us whether anything changes. The whole point is the longitudinal picture. None of these pieces produces a useful answer on its own.

Three things, one ongoing relationship.

If your Chihuahua has been tested by Embark on or after October 2024, you can become part of the dataset by sending us three things: the full Embark PDF, a current liver panel from your veterinarian, and a follow-up liver panel every one to two years. There is no fee. You can withdraw at any time. We accept reports from pet owners, breeders, and rescue organizations alike.

Submit to

healthresearchataa@gmail.com

Required subject line

ATP7B Study - Embark Report + Liver Panel Submission

Required at intake

What we need on first submission, in one email.

Subject line is required. The research inbox receives submissions for multiple studies. Without the study name in the subject line, your submission risks being delayed or routed to the wrong dataset. Please use the exact subject line shown above (or click the email link to have it filled in automatically).

The full Embark PDF is required. We need every page so we can verify the test number, confirm 100% Chihuahua breed identification, and capture the ATP7B result alongside the rest of the panel.

A liver panel is required. A standard veterinary chemistry panel from a routine well-dog visit is sufficient. Most include the values we need (ALT, ALP, GGT, bilirubin, total protein/albumin). A bile acids test is welcome if your vet has run one but is not required. The panel should be reasonably current: within the past twelve months is ideal.

Required ongoing

A follow-up liver panel every 1 to 2 years.

This is what turns the dataset from a snapshot into a study. If the ATP7B variant has any subtle long-term effect on liver function in Chihuahuas, it will only become visible by tracking the same dogs over time and watching their liver values move (or, more likely based on what we have seen so far, stay stable). A single panel cannot show change. Repeated panels can.

You do not need a separate vet visit just for this: the liver panel run as part of your dog's annual or biennial wellness exam is exactly what we need. Just forward us the result when it comes back. Use the same subject line and reference your dog's call name so we can match the follow-up to the existing record.

  1. 01

    Use the required subject line

    "ATP7B Study - Embark Report + Liver Panel Submission". The email link above will fill it in automatically. The subject line is what tells us which study to file your submission under.

  2. 02

    Confirm the Embark test was October 2024 or later

    The ATP7B panel was added in late October 2024. Earlier reports do not contain the result. If you are unsure, send the report anyway. We will check.

  3. 03

    Download the full Embark PDF

    Log in at embarkvet.com → My Dogs → select your dog → Download PDF Report. We need every page Embark provides: health panel, breed identification, ancestry, traits, and the test ID.

  4. 04

    Get (or grab) a current liver panel

    A standard chemistry panel from a routine vet visit, ideally within the past twelve months. If you don't have one on hand, request a copy from your vet. They keep them on file. Most clinics will email it directly to you.

  5. 05

    Attach both PDFs to one email

    Send to healthresearchataa@gmail.com with the required subject line. One dog per email is easiest. Tell us briefly: call name, age, country, registry, and whether you are a breeder, owner, or rescue.

  6. 06

    Plan to send a follow-up liver panel every 1–2 years

    When your dog has their next annual or biennial wellness exam, forward the new liver panel using the same subject line and your dog's call name. That is the single most valuable thing any participant can do for this study.

  7. 07

    That is it

    We will confirm receipt, log the report under our verification protocol, and notify you if we have any questions. Your dog's record will live in the dataset under the call name you provided.

Frequently asked

Questions we hear most often.

My dog tested positive for two copies. Is my dog sick?

There is no evidence in our dataset, or in any published Chihuahua-specific research that we are aware of, that two copies of the ATP7B variant cause clinical disease in this breed. None of the homozygous dogs in our records has shown symptoms. That said, we are not your veterinarian and this study is not medical advice. If you have specific concerns, talk to your vet, and if you have any bloodwork on your dog, we would welcome it for the study. Your dog's data could help answer a question that is currently unanswered.

If the variant doesn't matter, why study it?

Because the question is unanswered, and someone has to do the work that answers it. The variant is now appearing on tens of thousands of Embark reports for Chihuahuas. Owners and breeders are already making decisions based on those results, sometimes panicked decisions. The honest, useful response is to gather verified data and report what we observe, including the absence of effects, until the picture is clear enough to draw a conclusion.

My Chihuahua has elevated liver enzymes. Is the ATP7B variant the cause?

Possibly, but not necessarily, and probably not provable from a DNA test alone. Copper-associated liver disease in dogs has two distinct causes: a primary genetic pathway and a secondary environmental pathway (most commonly excess dietary copper from modern commercial dog food, which has had higher bioavailable copper content since 1997). The two can look clinically similar but are diagnosed differently, typically requiring a liver biopsy with copper distribution analysis to tell apart. Cases of copper-related hepatopathy are rising in breeds with no identified genetic predisposition, which strongly suggests diet alone can produce the picture. If your dog has liver findings, please work with your veterinarian to identify the cause rather than assuming it's the variant.

Why do I need to submit a liver panel? Isn't the Embark test enough?

The Embark test tells us what variant your dog carries. The liver panel tells us whether anything is happening clinically. The whole point of this study is to determine whether the ATP7B variant in Chihuahuas correlates with liver changes, and that question simply cannot be answered from a DNA result alone. We need to see actual liver values, ideally tracked over time, to know whether the variant is doing anything in this breed. A standard chemistry panel from your dog's annual wellness exam includes the values we need (ALT, ALP, GGT, bilirubin) and is sufficient. You don't need to schedule a special vet visit. The next routine bloodwork will do.

My dog also has the "ALT Activity (GPT)" variant. Does that matter?

Yes, and it's worth flagging in your submission. The ALT Activity (GPT) variant gives carrier dogs a naturally lower baseline ALT, meaning their liver enzymes can read as "normal" on standard veterinary reference ranges even when subtle liver changes are happening. Embark notes this on the report. For our study, dogs with both the ATP7B variant and the ALT Activity variant are particularly informative, because their bloodwork needs to be interpreted against their personal baseline rather than the lab's standard range. Please mention it in your email if your dog has it.

How long is the ongoing follow-up commitment?

As long as you want it to be. The study is designed as a long-term registry, so we will accept follow-up panels for the lifetime of any participating dog. Realistically, what we are asking is that when your dog has their normal annual or biennial wellness exam, you forward the resulting liver panel to the research email. Most owners run wellness bloodwork anyway. You are not signing a contract. You can stop participating at any time, and removal of your dog's data is available on request.

My dog tested before October 2024. Can I still participate?

Not for this specific variant. The ATP7B panel did not exist on Embark's standard screen before that date, so older reports do not contain the result we are tracking. Embark allows you to upgrade older tests to the current panel for a fee, and once the upgraded result is available we welcome the report. Older reports may also be useful for our other research, so feel free to send them along anyway.

Why do you call it "two copies" instead of "affected" like Embark sometimes does?

Because "affected" is a clinical term and the clinical correlation has not been established in this breed. "Two copies" is what the genetic test actually tells us: the dog is homozygous for the variant. Whether that translates to disease is exactly the question we are studying. Until we have the data to answer it, using clinical language would be premature.

Should breeders remove carriers and two-copy dogs from their programs?

No, and at this stage of the evidence, doing so would likely cause more harm to the breed than the variant itself. Two-thirds of tested Chihuahuas carry at least one copy of the ATP7B variant. Eliminating them all would collapse genetic diversity in a breed that already has a relatively narrow founding gene pool, and it would be done in exchange for an unproven and possibly nonexistent benefit, since the variant's clinical relevance to Chihuahuas has not been established. The responsible path is informed pairing: a carrier bred to a clear dog produces no homozygous offspring, and frequency can be reduced over generations without removing dogs from the gene pool. We cover this in detail in the "On breeding decisions" section above.

Will my dog appear in the published study?

If you submit a report, your dog will be part of the dataset under their call name and Embark test number, the same identifiers Embark itself uses on the PDF. No owner names, addresses, or contact information are ever included in published findings. If you prefer your dog to appear anonymized (with only the test number), say so in your email and we will mark the record accordingly.

Is this affiliated with Embark, the AKC, or the CCA?

The study is independent. It is led by Rev. T. Stringer, FCG, M.Div, a Forensic Certified Genealogist. It uses Embark's PDF reports as primary source documents but is not run by, funded by, or formally affiliated with Embark. A research collaboration proposal has been shared with Embark separately.

Privacy & data use

Your dog's data is handled with care.

What we record

Call name, registered name (if any), Embark test number, test date, country, registry, ATP7B genotype, and any health information you choose to share. Nothing more than what you send us.

What we never share

Owner names, addresses, phone numbers, email addresses, payment information, or any personally identifying detail beyond what you choose to include. Owner identity is not part of the published dataset.

Citation & credit

Dogs are cited in publications by call name and Embark test number, the same identifiers Embark itself uses. Breeders and owners may request acknowledgement in any paper. Anonymity is also available on request.

Withdrawal

You may request removal of your dog's data from the active dataset at any time before publication. Once a paper is preprinted or published, removal becomes more limited. We will explain what is possible at the time of request.

Alfheim-Andromeda Chihuahuas

Where Science Meets the Soul of the Chihuahua