Miniature American Shepherd
The tested variant with the highest allele frequency is MDR1, at 12% among the 1,476 Miniature American Shepherds tested (Donner 2023; gene copies, not dogs), then Progressive Rod-Cone Degeneration (9.8%) and Degenerative Myelopathy (3.7%).
Which disease variants turn up in Miniature American Shepherds?
From a panel of 250 Mendelian-disease variants screened in 1,054,293 dogs (Donner et al. 2023), 15 turn up in Miniature American Shepherds at observable frequency. The figure beside each is its allele frequency. Of the gene copies tested in this breed, the share that carry the variant. Every dog carries two copies, so this is not the share of dogs. It is not clinical risk. Most recessive variants require two copies for disease expression; many dominant variants show incomplete penetrance. Read this as a population fingerprint of what's in the gene pool, not a per-dog prediction.
ABCB1what this gene does
ABCB1 is a gene that helps control how certain drugs are processed and cleared from a dog's body.
For your dog: If your dog is from a breed that carries this gene variant, ask your vet about medication sensitivities before giving any new drugs.
FGF4what this gene does
FGF4 influences leg length by affecting bone growth, leading to shorter legs in certain breeds.
For your dog: If your dog is from a breed known to carry this gene, it's worth discussing spinal health with your vet, but being a carrier doesn’t guarantee problems.
PRCDwhat this gene does
PRCD is a gene involved in the health of a dog's retina, the part of the eye that detects light and helps with vision.
For your dog: If your dog belongs to a breed known to carry PRCD changes, it's worth discussing eye health and potential genetic testing with your vet.
SOD1what this gene does
SOD1 is a gene that helps protect cells from damage caused by harmful molecules called free radicals.
For your dog: If your dog is a carrier of SOD1 variants, it's worth discussing with your vet, but remember carrier status doesn't mean your dog will get the disease.
PDK4what this gene does
PDK4 helps regulate how cells use energy, especially in the heart muscle.
For your dog: If your dog is one of the breeds known to carry this gene, it’s worth discussing heart health with your vet, but being a carrier doesn’t mean your dog will develop disease.
RPGRIP1what this gene does
RPGRIP1 is a gene involved in the function of photoreceptor cells in the eye, which help dogs see in different light conditions.
For your dog: If your dog belongs to a breed known to carry RPGRIP1 mutations, it’s worth discussing with your vet to understand the risks and monitor eye health.
NHEJ1what this gene does
NHEJ1 is a gene involved in repairing breaks in DNA, helping maintain the integrity of genetic information in cells.
For your dog: If your dog belongs to one of the breeds known to carry this gene variant, it's worth discussing testing with your vet to understand any potential eye health risks.
BEST1what this gene does
BEST1 is a gene that helps maintain the health of the retina, the light-sensitive layer at the back of the eye. It plays a role in keeping the cells in the retina functioning properly.
For your dog: If your dog is from a breed known to carry BEST1 variants, it’s worth discussing retinal health with your vet, especially if you notice any vision changes.
SLC2A9what this gene does
SLC2A9 is a gene that helps regulate uric acid levels in a dog's body. It plays a role in how the kidneys handle this substance.
For your dog: If your dog is one of the breeds known to carry this gene variant, it’s worth discussing with your vet to understand any potential urinary health concerns.
CUBNwhat this gene does
The CUBN gene helps the body absorb vitamin B12 from the intestines, which is essential for energy and nerve function.
For your dog: If your dog’s breed is on the list, it’s worth discussing CUBN-related risks with your vet to keep an eye on their vitamin B12 levels.
ADAMTS17what this gene does
ADAMTS17 is a gene that influences body size and also plays a role in certain eye conditions. It affects the structure of tissues in the eye and elsewhere in the body.
For your dog: If your dog belongs to a breed known to carry ADAMTS17 variants, it’s worth discussing genetic testing and eye exams with your vet to stay ahead of potential issues.
Full ADAMTS17 gene page →What these results mean for a Miniature American Shepherd
11.9% of Miniature American Shepherds in the Donner 2023 cohort carried it (n=1,476).
- MDR1 is a drug sensitivity, not a disease. A dog with the variant lacks a pump that keeps certain drugs out of the brain.
OMIA 001402-9615
“Multidrug resistance 1 is caused by a lack of P-glycoprotein drug transporter in the blood-brain barrier, which is characterized by neurotoxicity after administration of certain drugs.” OMIA 001402-9615
- Heartworm prevention is safe. At the dose on the label, every FDA-approved heartworm preventive sold in the United States is safe even for a dog with two copies of the variant.
Mealey 2008
“at the manufacturer's recommended dose, all FDA-approved heartworm preventive products marketed in the United States are safe, even for dogs with the ABCB1 mutant/mutant genotype” Mealey 2008
- The risk is dose. The same drug family (ivermectin, milbemycin and their relatives) causes toxicity in these dogs at doses other dogs tolerate, and some chemotherapy drugs are handled by the same pump.
Mealey 2008
“renders affected animals extremely susceptible to toxicosis induced by substrate drugs, such as the macrocyclic lactones at doses well below those tolerated by dogs with the wild-type ABCB1 gene” Mealey 2008
“Many drugs used in veterinary medicine are substrates for P-gp, including many chemotherapeutic agents and macrocyclic lactones” Mealey 2008
What to do
Keep heartworm prevention going at the label dose. Tell your veterinarian the dog's MDR1 status before any off-label parasite treatment or chemotherapy.
No test, or a mix
No test yet, or a mix that may have herding ancestry: label-dose heartworm prevention is safe either way. For any higher-dose decision, tell your veterinarian the dog is untested so it can be treated as a possible carrier.
1.6% of Miniature American Shepherds in the Donner 2023 cohort carried it (n=1,471).
- Two extra copies of a growth gene, FGF4, shape dog legs and spines. The one on chromosome 12 is the one tied to disc disease; the one on chromosome 18 shortens legs.
OMIA 000157-9615
“Two FGF4 retrogenes (FGF4L1 on chromosome 18 and FGF4L2 on chromosome 12) have been identified to cause dwarfism across many dog breeds.” OMIA 000157-9615
“Brown et al. (2017) reported that an FGF4 retrogene insertion in chromosome CFA12” OMIA 000157-9615
- Carrying it raises risk. It does not say which dog will have a disc problem. In Dachshunds researchers found the test is not a valid risk indicator on its own.
OMIA 000157-9615
“the FGF4 retrogene insertion on CFA12 is not a valid risk indicator on its own” OMIA 000157-9615
What to do
Ask your veterinarian what a carrier result changes for your dog. What lowers risk in a carrier is not established in the sources this page draws on.
No test, or a mix
Without a test nobody can say whether a dog carries it. Leg length alone does not tell you: the disc-disease copy and the short-leg copy are different insertions.
3.7% of Miniature American Shepherds in the Donner 2023 cohort carried it (n=1,476).
- DM is a loss of function in the spinal cord that begins in adulthood and progresses to paralysis of the back legs. There is no treatment that stops it.
OMIA 000263-9615
“This is an adult onset degeneration of the spinal cord that progresses to paraplegia and tetraparesis. There is no successful treatment. A genetic test is available.” OMIA 000263-9615
- Two copies of the SOD1 variant mean at risk, not affected. Some dogs with two copies never show signs.
OMIA 000263-9615
“some homozygous mutant dogs had no signs of degenerative myelopathy, which suggests incomplete penetrance or other causative loci” OMIA 000263-9615
- One copy makes a dog a carrier. In the study that found the variant, every affected dog tested had two copies.
OMIA 000263-9615
“All affected dogs tested were homozygous mutant.” OMIA 000263-9615
What to do
A DNA result is not a diagnosis. Take the result, and any change in how the dog walks, to a veterinarian.
No test, or a mix
Without a test nobody can say how many copies a dog has. A breed's allele frequency describes the breed, not this dog.
3.1% of Miniature American Shepherds in the Donner 2023 cohort carried it (n=1,476).
- This is a marker, not an established cause. The curated record says a test based on it is not a good indicator of heart disease risk even in Dobermans, the breed it was found in.
OMIA 000162-9615
“it is evident that any DNA test based on this marker will not be a good indicator of liability to this disorder in Dobermans” OMIA 000162-9615
What to do
A carrier result for this marker is not, on its own, a reason for heart screening. Heart screening is a conversation with your veterinarian about the breed and the dog.
No test, or a mix
What this marker means in breeds other than the Doberman is not established in the sources this page draws on.
For researchers Population genetics, disease models and every recorded condition Open the research detail for the Miniature American Shepherd
Where every number on this page came from.
This page draws on one primary data source. Allele frequencies and sample sizes come from Donner et al. 2023 (CC-BY-4.0), a direct-to-consumer screening cohort, graded Limited as a study design because the dogs were tested at their owners' choice. No genotyped research dogs of this breed are in the three open releases the atlas reads, so the population-genetic sections other breed pages carry are absent here for that reason, not hidden. Conditions recorded for the breed come from OMIA.
What this page does not yet have. Inheritance modes and per-disease penetrance evidence from Donner 2023 are in the structured data for every variant the panel covers. Mondo, OMIM, Ensembl, and HGNC cross-references live on the gene and disease pages this page links to, rather than being repeated here. What is still absent from this breed page is anything not in the cited panel, and each such gap carries its cause where it appears.
How to cite this page. Cite Donner et al. 2023 (doi:10.1371/journal.pgen.1010651) for every frequency on this page, and OMIA for each condition, with the sample size shown beside the figure.
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- Donner J, Freyer J, Davison S, Anderson H, Blades M, Honkanen L, et al. (2023). Genetic prevalence and clinical relevance of canine Mendelian disease variants in over one million dogs. PLOS Genetics 19(2):e1010651. doi:10.1371/journal.pgen.1010651
- Brundage DM (2026). CanVAS: A Harmonized and Imputed Canine Variant Atlas. bioRxiv. doi:10.64898/2026.04.13.718238
- Nicholas, F.W., Tammen, I., & Sydney Informatics Hub. (2026). Online Mendelian Inheritance in Animals (OMIA) [dataset]. The University of Sydney. https://omia.org. doi:10.25910/2AMR-PV70 (retrieved April 2026).