Mastiff
Mastiffs have a cited life expectancy of 9 years (McMillan 2024 / VetCompass, n=1,840, 95% CI 8.9 to 9.2). The tested variant with the highest allele frequency is Canine Multifocal Retinopathy 1, at 18% among the 767 Mastiffs tested (Donner 2023; gene copies, not dogs), then Cystinuria Type I-A (14%) and Degenerative Myelopathy (8.4%). 32 dogs stand behind the atlas figures here, so treat this page as an early sketch.
Also known as English Mastiff and Old English Mastiff.
Which disease variants turn up in Mastiffs?
From a panel of 250 Mendelian-disease variants screened in 1,054,293 dogs (Donner et al. 2023), 6 turn up in Mastiffs 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.
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.
SLC3A1what this gene does
SLC3A1 is a gene that helps transport certain amino acids in the kidneys. It plays a key role in preventing the buildup of cystine, which can form stones.
For your dog: If your dog is from a breed known to carry SLC3A1 variants, it’s worth discussing cystinuria risks with your vet, especially if urinary issues arise.
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.
SLC7A9what this gene does
SLC7A9 is a gene that helps transport certain amino acids in the kidneys. It plays a role in how the body handles cystine, an amino acid that can form crystals.
For your dog: If your dog is a carrier, it’s worth discussing with your vet to monitor urinary health and catch any issues early.
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.
What these results mean for a Mastiff
About 14 in every 100 copies of this gene in the 767 Mastiffs tested carry this change (Donner 2023).
- The kidneys can't hold on to cystine, one of the building blocks of protein. It can form crystals and stones that block the flow of urine.
OMIA 000256-9615
“Cystinuria, type 1 - A is an inherited defect that causes failure of reabsorption of cystine in the proximal renal tubule, leading to cystine precipitation in the urine. Formation of crystals and calculi lead to urolithiasis and urinary tract obstruction.” OMIA 000256-9615
What to do
If your dog is straining to pee, or passing little or none, see a vet the same day.
Not tested, or a mix
Without a test, no one can tell how many copies your dog has.
About 8 in every 100 copies of this gene in the 767 Mastiffs tested carry this change (Donner 2023).
- DM slowly damages the spinal cord in adult dogs, until the back legs stop working. Nothing yet can stop 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 gene change mean a dog is at risk, not that it will get sick. Some dogs with two copies never do.
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 this change, every dog with DM that was tested had two copies.
OMIA 000263-9615
“All affected dogs tested were homozygous mutant.” OMIA 000263-9615
What to do
A DNA result isn't a diagnosis. If the way your dog walks changes, take that and the result to your vet.
Not tested, or a mix
Without a test, no one can tell how many copies your dog has. How common it is in a breed says nothing about one dog.
A bladder-stone (cystinuria) test that doesn't hold up
Not a reliable testAbout 3 in every 100 copies of this gene in the 767 Mastiffs tested carry this change (Donner 2023).
- Some DNA tests check this gene change for bladder stones. The researchers who studied it found it doesn't cause them, and they advise against using it as a test.
OMIA 001880-9615
“there appears to be no support for the variant to be causal” OMIA 001880-9615
“strongly recommend not to use "the variant in SLC7A9 as a test to predict the risk of developing cystinuria in male English bulldogs.” OMIA 001880-9615
What to do
A result for this change, either way, tells you nothing about bladder stones. If your dog strains to pee or there's blood in the urine, see a vet, whatever a DNA test said.
Not tested, or a mix
Nothing to do. There's no reason to test for this one.
Other names
The Mastiff is also recorded as English Mastiff and Old English Mastiff.
Identified as Mastiff (VBO:0200867) in the Vertebrate Breed Ontology (Mullen et al. 2025, CC-BY 4.0) · registry IDs FCI 264 · iDog 157 · VeNom 14368.
For researchers Population genetics, disease models and every recorded condition Open the research detail for the Mastiff
In the atlas, the Mastiff clusters consistently as Mastiff (100% of the 32 dogs here). Dogs here sit in a relatively sparse region of the atlas, fewer close neighbors than typical.
Life expectancy in the VetCompass cohort (McMillan 2024, n=1,840) is 9 years, about 2.1 years shorter than the atlas size trend predicts for the breed, one of the larger gaps in the atlas.
What the atlas genotypes say about Mastiff
Computed from the 14,478 CanVAS dogs in the Atlas, on an imputed genotype backbone: 77,215 directly typed sites per dog, imputed to 9.67 million variants.
The confidence below counts dogs, not reads: it is the size of the sample, and it is separate from how the genotypes were measured.
What does genetic diversity mean?
How varied a breed's gene pool is — the share of gene spots where a typical dog of the breed carries two different versions rather than two identical ones.
How to read it: Higher = more diverse. Among well-sampled breeds it ranges roughly 0.22 (least diverse) to 0.33 (most diverse).
Diversity is a strength, not a verdict on any individual dog. Lower diversity means it's worth paying attention to recessive-risk testing — not that a dog is doomed.
What does within-breed variation mean?
How much individual dogs within the breed differ from each other genetically.
How to read it: Higher = more internal variety among individuals of the breed.
Sensitive to how many dogs of the breed we've sampled.
What does typical lifespan mean?
The median age dogs of the breed tend to reach.
How to read it: Higher = longer-lived. Compare to longevity-for-size to see whether it's just a size effect.
Drawn from population lifespan records; individual dogs vary widely with care, genetics, and luck.
Every condition recorded in the Mastiff
Beyond the testable carriers above, OMIA's literature catalogue records 3 genetic conditions in the Mastiff. This is the documented landscape across all Mastiffs ever studied, not a prediction for any one dog.
Where every number on this page came from.
This page draws on three primary data sources. Allele frequencies for the Mendelian section come from Donner et al. 2023 (CC-BY-4.0). We grade these data at evidence Limited because the cohort is a direct-to-consumer ascertainment, which biases toward owners who chose to test their dogs. The panel also uses tag-SNP proxies for some variants rather than direct causal-variant assays. Limited is a study-design grade, not a quality grade: the Donner cohort is the largest open canine-genotype dataset in existence and we are grateful for it. We rate the confounding MEDIUM.
Population-genetic dimensions (heterozygosity, intra-breed PCA distance, nearest neighbors, trait-locus frequencies) come from CanVAS (Brundage 2026), harmonized through the Sniff Atlas. The exact release date and verification commit are pinned at the bottom of the page so a researcher can trace a number back to a specific snapshot. The disease-gene-variant graph comes from OMIA (Online Mendelian Inheritance in Animals; Nicholas, Tammen, and the Sydney Informatics Hub at the Sydney School of Veterinary Science, The University of Sydney; retrieved April 2026, DOI 10.25910/2AMR-PV70).
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. The computed dimensions on this page are derived from the open Sniff Atlas v1.0.2 (Gehring 2026, doi:10.5281/zenodo.20566358, CC-BY 4.0). Full citation formats including BibTeX, RIS, and CITATION.cff at sniff.world/cite.
Some things about living with a mastiff never make it into a database. Add what you know as a Keeper, in your words →
Lived experience, kept beside the science.We have 33 mastiffs. We do not have yours.
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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).