Neapolitan Mastiff
12 Neapolitan Mastiffs in the atlas. Every number on this page has a source.
12 Neapolitan Mastiffs in the Sniff Atlas. Population-genetic snapshot, Mendelian carrier frequencies from Donner 2023, and the data substrate's release version, sample sizes, and evidence tier on every claim.
In the atlas, the Neapolitan Mastiff clusters consistently as Neapolitan Mastiff (100% of the 12 dogs here). Genetic diversity is high (mean heterozygosity 0.3294), reflecting either a mixed-breed cluster or breeds with broad genetic backgrounds. At the trait loci, LCORL runs lower than average (0% here vs 83%); KRT71 runs lower than average (21% here vs 91%). Dogs here sit in a relatively sparse region of the atlas, fewer close neighbors than typical.
Mean heterozygosity is 0.329, notably high, indicates broad genetic background. Only 12 dogs of this breed in the atlas, modestly sampled.
Closest genetic neighbors in the atlas: Cane Corso, Saint Bernard, Mastiff, Newfoundland, and Great Dane.
What the genome says about Neapolitan Mastiff
Computed from the 18,477 research dogs in the Atlas.
- Cane Corso4.10
- Saint Bernard8.09
- Mastiff9.06
- Newfoundland9.35
- Great Dane9.47
Frequency of the alternate allele in this breed at each locus's representative SNP.
| IGF1 | 55% |
| HMGA2 | 83% |
| SMAD2 | 83% |
| LCORL | 0% |
| STC2 | 44% |
| ADAMTS17 | 55% |
| FGF4·CFA18 | 100% |
| FGF4·CFA12 | 83% |
| RSPO2 | 56% |
| FGF5 | 50% |
| KRT71 | 21% |
| MC1R | 79% |
| MSRB3 | 100% |
| BMP3 | 100% |
| SMOC2 | 67% |
What does the genome say about how a Neapolitan Mastiff looks?
Neapolitan Mastiffs look the way they do because of a small set of fixed and near-fixed morphology genes that, taken together, define the visible breed. Each translation below pairs the gene with the trait an owner actually sees, the breed's allele frequency at that locus, and a one-clause causal phrase.
Size and build
IGF1 sits at 55% for the small-body allele. IGF1 is the gene that sets dog body size from Chihuahua to Great Dane. Intermediate frequencies typically keep a breed in the mid-sized range rather than tipping toward the larger working forms.
HMGA2 sits at 83%. HMGA2 is a chromosome-10 size locus that acts together with IGF1, and intermediate frequencies reflect partial commitment to the dominant size variant.
SMAD2 sits at 83% at the chromosome-7 height locus.
LCORL is at 0%, the NCAPG/LCORL height locus running against the breed's body-size profile here.
STC2 sits at 44%.
ADAMTS17 sits at 55%. ADAMTS17 is a body-size locus also linked to lens disorders.
Leg length
The FGF4 retrogene on chromosome 18 is near-fixed in this breed at 100%. This is the leg-length variant. The breed is fully committed to the long-legged form rather than the short-legged Corgi-and-Dachshund body plan.
The FGF4 retrogene on chromosome 12 sits at 83%, the chondrodystrophic variant.
Coat type, length, and color
RSPO2 sits at 56% for the furnishings variant. Furnishings (the eyebrow-and-mustache pattern seen in Schnauzers and Wheaten Terriers) vary across the population at this intermediate frequency, and visible expression depends on the specific allele combination each dog carries.
FGF5 sits at 50% for the long-coat variant. Coat length is influenced by other loci as well, so intermediate FGF5 frequencies do not always correspond to intermediate visible coat lengths.
KRT71 is at 21% for the wavy/curly variant, leaving the breed's coat straight.
MC1R sits at 79% at the representative SNP. MC1R controls the switch between red-to-gold pigment and black-to-brown pigment, with the e/e homozygous genotype producing the gold-to-red spectrum. Substrate frequencies at this SNP depend on the array's polarity, so visible coat color in the breed is a more reliable indicator than this single number.
Ears
MSRB3 is at 100% for the drop-ear allele, the genetic basis of the breed's signature dropped ear set.
Skull shape
BMP3 is at 100%, contributing to the breed's brachycephalic skull shape.
SMOC2 sits at 67%, contributing to the breed's moderate head shape.
What genetic diseases do Neapolitan Mastiffs carry?
From a panel of 250 Mendelian-disease variants screened in 1,054,293 dogs (Donner et al. 2023), Neapolitan Mastiffs carry 5 of them at observable frequency. Carrier frequency 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.
Where every number on this page came from.
This page draws on three primary data sources. Carrier 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 now in the structured data for every variant the panel covers. Mondo, OMIM, Ensembl, and HGNC cross-references on gene pages remain pending — they arrive in December 2026 alongside the imputed 9.67M-variant CanVAS dataset via the OMIA SQL dump absorption. Until then, gene IDs carry NCBI Gene and OMIA phene URLs only; the wider human-homolog and disease-ontology cross-reference set fills in with that release.
How to cite this page. The computed dimensions on this page are derived from the open Sniff Atlas v1.0.1 (Gehring 2026, doi:10.5281/zenodo.20566358, CC-BY 4.0). Full citation formats including BibTeX, RIS, and CITATION.cff at sniff.world/cite.
We have 12 neapolitan mastiffs. We do not have yours.
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- Donner J, Anderson H, Davison S, et al. (2023). Frequency and distribution of 152 genetic disease variants in over 1,000,000 mixed-breed and purebred dogs. PLOS Genetics 19(2):e1010651. doi:10.1371/journal.pgen.1010651
- Brundage J, et al. (2026). CanVAS: a harmonized 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).