Miniature Bull Terrier Health Problems, and the Tests That Screen for Them

The US breed club says it plainly: miniature bull terriers "are generally healthy dogs", but there are health issues that owners and buyers should know about. This guide goes through those issues one at a time. For each one you get what it is, how it's screened, who does the screening, and the document a breeder should be able to put in front of you.

We're a kennel and we sell puppies, so read this with that in mind. Everything below is sourced to breed clubs, registries, testing bodies or peer-reviewed studies, linked in the text and listed at the end.

Summary table: condition, test and the document to ask for

This table puts together what the Miniature Bull Terrier Club of America (MBTCA), the UK's Miniature Bull Terrier Club, The Royal Kennel Club and the Orthopedic Foundation for Animals (OFA) publish. The two national clubs don't screen in exactly the same way, and the differences are noted.

If you want one number to ask about in the US, it's the CHIC number. The MBTCA explains that a dog with CHIC certification has clearances for heart, hearing and kidney issues from the OFA, plus an eye clearance. A CHIC number means the tests were done and the results were made public. It doesn't mean every result was perfect.

Primary lens luxation (PLL): the DNA test

What it is. PLL is an inherited eye disease in which the fibres holding the lens in place break down, so the lens slips out of position. The Royal Kennel Club describes it as "a well-recognised, painful and blinding inherited eye condition", with complete luxation typically between 3 and 8 years of age.

How it's screened. PLL is caused by a known mutation in the ADAMTS17 gene and is inherited as an autosomal recessive trait. That makes it the easiest problem on this list to screen for. One DNA test gives a definite genotype for life: clear, carrier or affected. The UK registry lists the PLL DNA test as a recommended pre-breeding test for the miniature bull terrier, and the US club requires its member breeders to test breeding dogs.

What each result means, how carriers can be bred safely and how to check a certificate take more space than this section has. There's a full guide: PLL clear, carrier and affected, explained.

Deafness: the BAER test, in white and coloured dogs

What it is. Congenital deafness is present from birth and can affect one ear (unilateral) or both ears (bilateral). A puppy that is deaf in one ear often behaves normally, so you can't reliably spot it at home. In one study of bull terriers (the standard breed, a close relative), white bull terriers were more likely than coloured ones to be deaf (Strain, The Veterinary Journal, 2004). The MBTCA adds that coloured mini bulls "have been known to be deaf as well", so a coloured coat is not a free pass.

How it's screened. The Brainstem Auditory Evoked Response (BAER) test measures the brain's electrical response to clicks played into each ear separately. The OFA calls it "the only accepted method of diagnosis". It can be done from 35 days of age, and a dog passes only with bilateral hearing: "Unilateral or bilateral deafness fails."

What to ask for. BAER results for both parents. If the litter has been tested, ask for the puppy's own result too, since this is the one screening that works at puppy age. MBTCA member breeders must BAER-test their breeding dogs. For more on why white dogs are over-represented, see our guide to white miniature bull terriers and deafness.

Kidney disease: hereditary nephritis and polycystic kidney disease

The US club calls kidney disease a "silent killer" because dogs may show no symptoms until their kidneys have failed. Two separate conditions are involved, each with its own screening.

Hereditary nephritis (familial nephropathy): the UPC test

Hereditary nephritis damages the kidney's filtering membrane, so protein leaks into the urine long before the dog looks ill. In bull terriers it's studied as a model of autosomal dominant Alport syndrome (Hood et al., 2002). The screening test is a urine protein:creatinine (UPC) ratio. A vet sends a urine sample to a lab, and the lab divides the protein value by the creatinine value.

The UK Miniature Bull Terrier Club gives specific guidance on its kidney disease page:

• test at 12 months, then every year for breeding dogs, with a current certificate before mating;
• the standard threshold is a ratio of 0.5. Australian research suggested 0.3 for the breed, but the Kennel Club hasn't endorsed that figure. Anything above 0.5 should be investigated;
• the sample should be mid-stream, first thing in the morning, before food, and free of blood or inflammation, which can give a falsely high result;
• a UPC "only tests the kidney function at that point in time and is not an indicator for future disease."

That last point matters to you as a buyer. A single UPC result from years ago tells you little. Ask for the most recent result, with its date.

Polycystic kidney disease (PKD): ultrasound

PKD causes fluid-filled cysts in the kidneys. In bull terriers it's inherited as an autosomal dominant trait, meaning one copy of the variant is enough. A 2011 study linked it to a variant in the PKD1 gene (Gharahkhani et al., PLoS One). That study was in (standard) bull terriers. The MBTCA's screening advice for mini bulls is a kidney ultrasound. The two kidney diseases can also appear together in the same dog (O'Leary et al., 2002).

Heart disease: auscultation, echo and colour Doppler

What it is. The UK club names the two main heart conditions in the breed as mitral valve dysplasia (MVD) and aortic stenosis (AS). Both are problems with heart valves. The MBTCA warns that untreated valve problems can lead to congestive heart failure, atrial fibrillation and early death.

How it's screened. This is where the two national clubs differ most:

In the US, the OFA's advanced cardiac database has required an echocardiogram by a board-certified cardiologist since October 2020, and official certification starts at 12 months of age.

What to ask for. The cardiologist's certificate for each parent, with a date. Also ask which method was used. An echo with colour Doppler shows more than a stethoscope, and a good breeder will tell you which one their dogs had.

Patellar luxation, laryngeal paralysis and lethal acrodermatitis

These three are documented in miniature bull terriers but aren't on the core screening lists above. Here's what the sources say, and no more.

Patellar luxation

The kneecap slips out of its groove, which can cause pain when walking. The MBTCA notes that surgery may be required in some cases. The screening is a hands-on vet exam. The OFA's patellar database is for dogs aged 12 months and over, and it recommends re-examination because some luxations only show later in life.

Laryngeal paralysis

The larynx fails to open properly when the dog breathes in, which can obstruct the airway. A 2019 study found an early-onset form in miniature bull terriers and identified a RAPGEF6 gene variant as a major risk factor. Dogs with two copies had a 10- to 17-fold increased risk. The authors describe an imperfect genotype-phenotype correlation, though. A result for this variant is a risk indicator, not a diagnosis.

Lethal acrodermatitis (LAD)

LAD is a severe inherited disease of bull terriers and miniature bull terriers, with poor growth, immune deficiency and skin lesions, especially on the paws. It's autosomal recessive. A 2018 study identified the causal variant in the MKLN1 gene and noted that this "facilitate[s] genetic testing" of both breeds. If a breeder says their dogs are LAD-tested, ask for the lab report, just as you would for PLL.

How to read a health report, and spot a fake one

A health test is only worth something if the paper in your hand really belongs to the dog you're being sold. Registries take this seriously. The Royal Kennel Club only records DNA results from approved laboratories, and the certificate must carry at least two forms of identification: the microchip or tattoo number plus the registered name or number.

Use the same standard yourself. For every report you're shown, check:

• Issuer. A named laboratory, veterinary practice, cardiologist or eye panellist, not a document typed by the breeder.
• Identity. The dog's microchip number, and ideally its registered name. Ask to see the microchip scanned on the video call and compare the digits.
• Date. DNA results are for life. UPC, heart and eye results are snapshots, and the UK club and eye schemes expect repeats at 12-month intervals.
• Method. For the heart: auscultation or echo with colour Doppler? For kidneys: UPC, ultrasound or both?
• The result in the issuer's own words. "Clear", "Normal", "Bilateral hearing", a UPC ratio number, a murmur grade.
• A way to check it independently. Some results are public. The OFA has a searchable database, the Royal Kennel Club has a Health Test Results Finder for dogs on its register, and it publishes a list of PLL-tested miniature bull terriers. For dogs registered elsewhere, you can contact the laboratory named on the certificate and ask it to confirm the result.

Health certificates are one of the documents scammers fake most often. If the paperwork looks generic, has no microchip number, or the breeder won't say which lab issued it, treat that as a warning sign. Our guide on puppy scams and fake health certificates covers the patterns in detail.

What our breeding dogs are tested for

Here is exactly what we state on our homepage. Our parents are DNA-tested for primary lens luxation, and the laboratory's own report is available to you.

For every other screening in this guide, ask us dog by dog on the call. If a result exists, we'll show you the document. If it doesn't, the honest answer is "not done", and that's the answer you should expect from us too. Apply the same test to every breeder you speak to.

Lifespan, and what health testing can't do

The American Kennel Club gives the breed's life expectancy as 11 to 13 years. Screening the parents lowers the odds of the inherited problems above. It doesn't remove them, and it says nothing about accidents, infections or diseases without a known test.

That's why the contract matters as much as the certificates. A written health guarantee, signed before any payment, tells you what happens if something does go wrong.

Frequently asked questions

Medical disclaimer. This article is general information about inherited conditions and screening programmes, compiled from the sources linked above. It is not veterinary advice and is not a substitute for examination by a veterinarian. If you're worried about a specific dog's eyes, hearing, kidneys, heart or breathing, see a vet, and for eye pain or sudden redness, see one urgently.

Sources

1. Miniature Bull Terrier Club of America, Health Issues.
2. Miniature Bull Terrier Club (UK), Kidney Disease and Heart Disease.
3. The Royal Kennel Club, Bull Terrier (Miniature) breed page, DNA test PLL, DNA testing, Eye screening scheme.
4. Orthopedic Foundation for Animals, Congenital Deafness, Cardiac Disease, Patellar Luxation, Eye Certification.
5. UC Davis Veterinary Genetics Laboratory, Primary Lens Luxation.
6. American Kennel Club, Miniature Bull Terrier.
7. Strain GM (2004). Deafness prevalence and pigmentation and gender associations in dog breeds at risk. The Veterinary Journal 167(1):23-32. PubMed 14623147.
8. Hood JC et al. (2002). Autosomal dominant Alport syndrome in Bull terriers. Nephrology Dialysis Transplantation 17(11):1897-908. PubMed 12401844.
9. O'Leary CA et al. (2002). Renal pathology of polycystic kidney disease and concurrent hereditary nephritis in Bull Terriers. Australian Veterinary Journal 80(6):353-61. PubMed 12153062.
10. Gharahkhani P et al. (2011). A non-synonymous mutation in the canine Pkd1 gene is associated with autosomal dominant polycystic kidney disease in Bull Terriers. PLoS One 6(7):e22455.
11. Hadji Rasouliha S et al. (2019). A RAPGEF6 variant constitutes a major risk factor for laryngeal paralysis in dogs. PLoS Genetics 15(10):e1008416.
12. Bauer A et al. (2018). MKLN1 splicing defect in dogs with lethal acrodermatitis. PLoS Genetics 14(3):e1007264.