Staffordshire Bull Terrier L-2-HGA (L2HGDH): AHT Research and 27 Dogs

SamOur young Staffie walks like his back legs are wooden. Is that just puppy clumsiness?

Elena MarshPossibly, but see a vet. In a 2016 Animal Health Trust survey of 27 affected Staffords, a stiff gait was usually the first sign owners noticed.

SamHis papers say “hereditary clear”. Doesn’t that rule out inherited brain problems?

Elena MarshIt covers one variant, often without swabbing the dog. In the Royal Kennel Club’s 2025 summary, about 95% of Stafford statuses for this test were inferred from parents.

SamIf it turned out to be something genetic, would that mean a short life for him?

Elena MarshNot necessarily. The same 27-dog survey found many dogs living for years after signs began, but your dog’s outlook is for a neurologist to judge.

Bottom line: L-2-hydroxyglutaric aciduria (L-2-HGA) is an autosomal recessive brain disease in which a faulty L2HGDH gene lets L-2-hydroxyglutaric acid build up in urine, blood and spinal fluid. The Staffordshire Bull Terrier is where veterinarians at the Animal Health Trust first described it (2001-2003), and where a 2007 University of Glasgow and Animal Health Trust study found the same two-letter change in exon 10 in all 21 affected dogs, and traced the pedigrees of 14 of them to a common ancestor. Signs usually start in the first year or two: stiff walking, tremor, behaviour change and seizure-like episodes. There is no cure, but in one owner survey 19 of 27 affected dogs were still alive a mean of 76.6 months after onset. A DNA result covers only the Stafford variant and is not a diagnosis; confirming L-2-HGA belongs to a veterinarian, usually with urine organic acid analysis and an MRI scan.

Madge, 2002, and the Newmarket reports that gave the disease its canine name

L-2-HGA began as a paediatric diagnosis. Dutch clinicians described the first patient in 1980, a five-year-old boy, under a title ending in a question mark: “an inborn error of metabolism?” By 2007, according to the Glasgow-led team, only about 100 human cases had been reported worldwide.

Dogs entered the story through the neurology department of the Animal Health Trust (AHT) in Newmarket, Suffolk. Carly Abramson, Laurent Garosi, Simon Platt and Jacques Penderis flagged a metabolic defect in Staffordshire bull terriers in a 2001 letter, and the Online Mendelian Inheritance in Animals database (OMIA) credits their 2001 and 2003 reports as the first animal cases of this inborn error. The 2003 clinical paper in the Journal of Veterinary Internal Medicine described six Staffords with seizures, ataxia, dementia-like change and tremor. L-2-hydroxyglutaric acid was raised in every body fluid tested. The authors called it the first veterinary model of this inborn error. At that point nobody knew which gene was at fault.

The breed’s own retelling of those years has a name in it. The Kennel Club’s genetics centre, in its spotlight on the Staffordshire Bull Terrier, recalls that in 2002 “a dog called Madge” was diagnosed with what was then termed L2 hydroxyglutaric aciduria, and that the Staffordshire breed council had already been collecting DNA samples and raising funds for the centre’s earlier hereditary cataract research, groundwork the L-2-HGA work could then build on.

SamSo owners and breeders actually paid for the research? That sounds like a rare thing.

Elena MarshIt is uncommon. The Canine Genetics Centre credits the breed council with samples and fundraising for its earlier cataract work; the L-2-HGA mutation was announced in 2005, two years before the 2007 paper.

Exon 10, one shared ancestor and a clean-up enzyme that stops cleaning

The paper that pinned down the cause appeared in the Journal of Medical Genetics in 2007. Its first author, Jacques Penderis, was at the University of Glasgow; most co-authors, including Cathryn Mellersh, were at the AHT. According to the Canine Genetics Centre, Mellersh had announced the mutation in 2005, together with the separate cataract mutation, so the test reached breeders before the journal article did.

The team worked with 21 affected Staffords and 127 related unaffected dogs from the UK pet population. In the eight affected dogs whose urine was quantified, mean L-2-hydroxyglutaric acid was 2,856 mmol/mol creatinine, against 3.12 in 25 controls, and stable-isotope gas chromatography confirmed that it was the L form rather than its mirror-image D form. Markers near L2HGDH, typed in 42 dogs, showed affected dogs with two identical copies of one chromosome stretch and obligate carriers with one, the signature of a recessive disease.

Sequencing then found the change: two single-letter substitutions in exon 10, separated by one unchanged base, which together swap two amino acids (leucine 433 to proline and histidine 434 to tyrosine). All 21 affected dogs carried it on both chromosomes; every carrier carried one copy. No dog was ever found with only one of the two substitutions, which suggested to the authors that both arose in a single event. Five-generation pedigrees of 14 affected and 34 carrier dogs, with extended records supplied by the Kennel Club, ran back to one common ancestor. That is a founder effect within those families, not proof that every Stafford alive descends from a single dog.

The same change appears under several labels. The 2007 paper wrote it on the old CanFam1.0 genome map as c.[1297T>C; 1299C>T]. OMIA updates it to the newer CanFam3.1 map as c.1298_1300delinsCTT, a single three-letter replacement spanning both substitutions. Wisdom Panel lists one T>C coordinate on chromosome 8. A buyer comparing lab pages should read these as one Stafford variant, not three.

Why does this gene matter at all? In people it was identified only in 2004, independently by two groups. Rzem and colleagues at the Université Catholique de Louvain in Brussels identified a mitochondrial, FAD-dependent enzyme that turns L-2-hydroxyglutarate back into alpha-ketoglutarate, and found mutations in its gene in three affected families. In the same year Topçu and colleagues mapped 21 patients from 15 Turkish families to the same gene, then called C14orf160, and found nine different mutations.

What makes L-2-HGA unusual is that L-2-hydroxyglutarate is not a step on any recognised metabolic pathway. As the 2012 University of Missouri paper explains, it is formed as a by-product when malate dehydrogenase acts on the wrong substrate, and the L2HGDH enzyme exists to convert this waste back into something useful. Belgian researchers call the disease “a defect of metabolite repair”: when the repair enzyme fails, the by-product accumulates and the brain bears the damage.

Cats now offer an unexpected cross-check on the Stafford change. In 2021 a Bern team found a single amino-acid change at position 434 of L2HGDH in a domestic longhair cat with the disease, the same position touched by the Stafford variant, and argued that altering histidine 434 alone is enough to disable the enzyme. The brain tumours reported in some human patients have not been described in affected dogs, and should not be read across to Staffords.

Stiff legs, staring spells and episodes: the 27-dog owner survey

The best picture of how the disease unfolds in Staffords comes from a 2016 study led by the Animal Health Trust neurology service with the Royal Veterinary College, Tay Valley Veterinary Centre and UC Davis. Questionnaires were sent to the owners of 119 dogs that had tested positive for the known L2HGDH variant; 27 came back, all describing dogs with neurological signs. Not every owner answered every question, so the denominators shift.

• Age at onset: mean 12 months, ranging from 2.5 to 60 months.
• Gait: abnormal in 26 of 26, with limb stiffness (24 of 26) the most frequent and usually the first thing noticed. A hunched back and body or head tremor were each reported in 19 of 26, and high-stepping, exaggerated limb movements in 15.
• Behaviour: changed in 24 of 27. Among 24 answers, 21 dogs stared into space, 17 showed dementia-like signs and 15 lost house-training.
• Episodes: 18 dogs had seizure-like or dyskinetic episodes.

A South African report adds a warning about subtle presentations. Writing from a referral hospital in Port Elizabeth, Böhm and colleagues described the country’s first published case, noted at least three more affected dogs identified by PCR, and observed that some dogs show only slight behavioural change. Affected dogs also had normal routine bloodwork and urinalysis, so a “normal” health screen does not exclude the disease.

Commercial labs quote wider onset windows than the survey mean. Embark says affected Staffords can present from 4 months to 6 years; Wisdom Panel says most present between six months and one year but some as late as seven years. Embark also uses the nickname “Staffy cramp”.

SamHe sometimes just stares at the wall for a minute. I assumed he was being a daft terrier.

Elena MarshIt may be nothing, yet staring into space featured in 21 of 24 answers in the 2016 survey. A dated phone video helps a vet far more than memory.

Urine, MRI and the pathologist’s slide: how a vet confirms L-2-HGA

A DNA test says whether a dog carries the Stafford variant; a diagnosis explains why a dog is unwell. The work-up combines three tools, each with its own blind spot.

Urine organic acids. Gas chromatography-mass spectrometry shows a very large excess of 2-hydroxyglutaric acid in affected dogs. A 2011 Vet Times review for UK practitioners quoted reported levels from 2,223 to 3,922 mmol/mol creatinine, with stated reference ranges all between 0.6 and 17. Ideally the lab also separates the L form from the D form, a different disorder. We did not find a UK veterinary laboratory publicly listing this analysis for dogs, so ask your vet or neurologist where they send samples.

MRI. In the 2007 study, 12 affected Staffords showed symmetrical bright signal on T2 and FLAIR images in the cerebral cortex, the junction between grey and white matter, the thalamus, the caudal colliculi and the cerebellar nuclei, with no contrast enhancement. A 2024 multicentre study across the UK, Switzerland, Spain, the Netherlands and the US reviewed 13 dogs with L-2-HGA, including Staffords, Yorkshire Terriers, Westies and crossbreeds, and found swollen cortical grey matter and enlarged brain volume in all of them, with the thalamus and caudal colliculi involved in every dog. People are different: an MRI study of 56 human patients found mainly frontal, subcortical white-matter damage.

Pathology. The only microscopic study in the breed, from the Royal Veterinary College, examined an 11-month-old Stafford confirmed by urine testing and DNA. The brain showed marked spongy change concentrated in grey matter of the cortex, thalamus, cerebellum and brainstem, and the swollen cells were astrocytes, the support cells of the brain.

A UK owner starts with the regular vet, who can refer on. The University of Glasgow Small Animal Hospital, Penderis’s institution in 2007, describes its seizure clinic as Scotland’s first, and lists urinalysis, brain MRI and spinal fluid analysis among the tests it routinely runs to find the cause of seizures. The Royal Kennel Club’s breed page points owners with health concerns to their vet or the breed health co-ordinator. MRI is the expensive part; one ManyPets plan, for example, caps CT/MRI and cruciate surgery at £1,000, so check your own policy’s imaging limit before a referral, not after.

One mix-up to avoid: a 2013 Australian report of a severe brain disease in American Staffordshire bull terrier puppies aged 6-8 weeks described a Leigh-like encephalopathy, and the authors excluded L-2-HGA. It is a different condition in a different breed.

Measured in years: what “progressive” has meant for affected Staffords

L-2-HGA is usually called a progressive disease, and there is no cure. The 2016 survey nevertheless found that 19 of the 27 dogs (70%) were still alive at the time of the questionnaire, a mean of 76.6 months after signs began, with a range of 12 to 170 months. L-2-HGA was the reason for euthanasia in six dogs. Euthanasia came a mean of 44 months after onset, although two of the eight euthanised dogs were put to sleep within a year of their first signs.

These come from 27 of 119 owners asked, and owners of dogs that died early may have been less likely to reply, so 70% is not a general survival rate. The authors still concluded that signs can be managed and some affected dogs may live a normal lifespan. Management is decided case by case by a veterinarian, usually with anti-seizure treatment when episodes occur; we found no controlled treatment trial in dogs, and nothing in the literature supports claims that diet or supplements cure the disease.

The research also leaves open whether every dog with two copies will show signs. The survey sampled only owners who returned forms, and in the one-million-dog Wisdom Panel dataset the single purebred dog with two copies has no clinical record attached. A dog found to carry two copies on a panel before any signs is a reason to involve a vet early, not a prognosis.

Fifteen years of results: why most “clear” Staffords were never swabbed

The Kennel Club approved official DNA schemes for L-2-HGA and hereditary cataract in January 2006, which meant results from approved labs went straight onto the registration database. According to the Vet Times review, 6,474 Staffords had been tested at the AHT between the test’s commercial launch in 2005 and 2011, and 16% of them were carriers or affected. Early testing probably over-sampled relatives of sick dogs, so that is not a population estimate.

Compare that with the Royal Kennel Club DNA Annual Summary 2025. Over its 15-year window, 39,696 Staffords hold an L-2-HGA status. Of those, 37,741 are “hereditary clear”, meaning the status was inferred because both parents were clear. Only 1,955 dogs have an actual laboratory result: 1,878 clear, 76 carriers and one affected. By our arithmetic, that is 3.9% carriers or affected among dogs actually tested, down from 16% in the AHT years, but measured on a different group. In 2025 alone, 2,811 statuses were recorded: 2,707 hereditary clear, 99 tested clear, five carriers and no affected dogs. A separate RKC list of individually tested Staffords, generated on 13 May 2026, contained 3,792 records going back to 2006.

Set that against registrations. The Stafford was the largest breed in the RKC’s terrier group in 2025 with 5,375 puppies registered, out of 14,963 terriers, having peaked at 7,499 in 2021. With roughly five thousand registrations a year and about a hundred dogs actually swabbed, the breed’s “clear” population now rests mostly on pedigree records.

In the Wisdom Panel study of more than 1.05 million customer dogs, mostly American, the 610 Staffords tested had an allele frequency of 1.48%. That is the share of gene copies, not of dogs; the share of carrier dogs would be roughly double, and customer dogs are not a random sample. No other purebred breed carried the variant, including 42,793 American Staffordshire Terriers, but 62 of the 78 single-copy dogs were mixed breeds. At the OFA, 555 Staffords have registered an L-2-HGA result, with one carrier.

The paused two-generation rule, Best Practice status and the end of Assured Breeders

Inferred clear status has a known weakness. When the Kennel Club announced in 2019 that hereditary clear would be limited to two generations unless parentage was DNA-verified, it gave reasons in plain terms: a dog can be wrongly listed as hereditary clear after a lab protocol failure, a pedigree error or incorrectly recorded parentage. The limit was set for January 2022, moved to January 2023, and then, in July 2022, paused; the existing policy would remain “for the foreseeable future”. We found no later announcement that the limit had been brought in. The RKC itself still strongly recommends that breeding dogs, including apparently clear lines, be retested every two generations.

For a puppy buyer the practical question is whether either parent was DNA-tested or both inherited their status on paper.

Where the test sits in the RKC’s priorities is also telling. In the Royal Kennel Club Health Standard, the Staffordshire Bull Terrier has no DNA test in the “Good Practice” column at all. The L-2-HGA test is listed under “Best Practice”, alongside the cataract test, elbow scoring and eye screening, a tier the RKC describes as important conditions that may be less common or still being understood.

Older advice to “buy from an Assured Breeder” is now out of date. The Assured Breeders scheme closed on 31 December 2024; the club said only five percent of registered puppies came from its members and that Find a Puppy would instead prioritise breeders who health test. In England, licensed breeders (three or more litters in 12 months) must also not breed from a dog whose genotype could harm its offspring. In the US, the L2HGA DNA test is a CHIC requirement for the breed, registered through the OFA.

SamSo when a breeder says “both parents are clear”, what should I actually ask to see?

Elena MarshAsk whether each parent has its own lab result. The RKC’s 2025 figures show 37,741 inferred statuses against 1,955 tested dogs, so it matters.

From Newmarket to Cambridge: who reads the Stafford variant, and what it cannot see

The lab that developed the test no longer exists. The AHT announced its closure in July 2020, and the Kennel Club Genetics Centre reopened at the University of Cambridge, still led by Cathryn Mellersh, taking more than 40,000 DNA samples with it. The test now reaches owners through several sellers. Prices below are as listed at the time of writing (October 2026).

• Canine Genetic Testing (CAGT), the testing service at the Cambridge address, lists the L-2-HGA test at £49.50 including VAT with a 1-2 week turnaround, for the Staffordshire Bull Terrier, Shortybull and Wallace Bulldog. Its Stafford bundle was showing £75.24 against a regular £99.00.
• LABOKLIN UK lists test 8125 at £48.00 including VAT, 2-3 weeks, from EDTA blood or a cheek swab, run twice per sample. Its Stafford KC bundle with the cataract test (8712) is £96.00, the same as two single tests.
• Embark (US) reads the Stafford variant only within its Breed + Health kit, $139 on sale against a regular $159, and labels the result “Provisional”. Wisdom Panel Premium is £144.99 on its UK site and includes the variant; Orivet lists a single test at $60.00 and Genomia at $56.00 excluding VAT.
• Animal Genetics lists its HGA test at £40.00 or $45.00 for Staffords and related breeds, but its only cited reference is the Yorkshire Terrier paper. The page does not say which variant it reads, so ask before ordering. The RKC lists this lab as “verification in progress”.

The RKC records results only from labs on its list, and the certificate must carry the microchip or tattoo number plus the registered name or number. Publication usually takes 5 to 10 working days, sometimes up to 28; a kit that cannot be recorded does little for a breeder.

The assays above, except possibly Animal Genetics, read the exon 10 change found in Staffords. Other forms of the disease involve different mutations. In Yorkshire Terriers, a 2012 University of Missouri study ruled out the Stafford variant first and then found a change in the start codon of the same gene, a result echoed by a separate group in Barcelona with two more Yorkies. In the Wisdom Panel data the Stafford variant was absent from 8,367 Yorkies. A West Highland White Terrier case reported from the AHT in 2005 still had no published genetic cause in 2012; a separate Westie variant from the Cambridge centre is listed only as a manuscript in preparation.

So a “clear” Stafford can still develop seizures or a stiff gait from idiopathic epilepsy, another inherited or metabolic brain disease, infection or injury, which is why the urine and MRI work-up matters even with a perfect DNA certificate. OMIA warns that a variant listed in its tables is not automatically fit for DNA testing outside the breed where it was found.

Insurance before the first stiff step

Because signs can appear from a few months of age, timing of cover matters. Agria’s policy booklet defines illness to include “defects and abnormalities your dog was born with or which were passed on by its parents”, and excludes conditions that first showed clinical signs before the policy started, as well as illness in the first 10 days of a new policy.

Staffords also sit close to a line some insurers draw. The Dangerous Dogs Act does not list the Staffordshire Bull Terrier, but Animal Friends excludes “American/Irish Staffordshire Bull Terriers” alongside the banned types, may ask for a breed DNA test at the owner’s expense, and voids a policy if the result shows more than 50% of an excluded breed. That is an ancestry test, not the L2HGDH test. Animal Friends treats a condition as pre-existing if it was first noticed before the start date or in the waiting period, treated or not.

In the US, Pumpkin names hereditary conditions among those it covers, with a waiting period of 14 days or less. Its route back to cover for a pre-existing condition applies only to curable conditions that stayed free of symptoms and treatment for 180 days; L-2-HGA is not curable, so signs noticed before enrolment would stay excluded. None of this guarantees a claim.

Frequently asked questions

Q. My Stafford is hereditary clear. Was he actually tested?
Probably not. Hereditary clear means the status was inferred from two clear or hereditary clear parents. In the RKC’s 15-year figures that applies to 37,741 of 39,696 Staffords with an L-2-HGA status. If you plan to breed, a direct test removes the doubt from pedigree or lab errors.

Q. How common is the variant in Staffords today?
No random population survey exists. Among dogs actually tested in the RKC’s 15-year window, 77 of 1,955 were carriers or affected (our calculation); in 610 mostly American Wisdom Panel customer Staffords, the allele frequency was 1.48%. Both are selected groups.

Q. Can a carrier be bred?
Testing services such as CAGT say carriers can be bred safely if the mate has been tested clear. Two carriers give each puppy about a one-in-four chance of being affected.

Q. My dog has odd episodes but tested clear. Could it still be L-2-HGA?
Unlikely if the Stafford variant was read correctly, but not impossible, and many other conditions cause seizures and stiffness. A clear result does not explain symptoms. Book a veterinary assessment.

Q. What happens when a dog is diagnosed?
A vet or neurologist confirms it with urine organic acid analysis, MRI and the DNA test, then manages signs such as seizures. There is no cure. Of 27 surveyed affected dogs, 19 were alive a mean of 76.6 months after onset, but outcomes vary.

Q. When is it an emergency?
A seizure lasting several minutes, or seizures one after another without recovery, needs an emergency vet straight away. Any new stiffness, tremor or behaviour change in a young Stafford deserves a prompt appointment.

References

• Penderis J, Calvin J, Abramson C, Jakobs C, Pettitt L, Binns MM, Verhoeven NM, O’Driscoll E, Platt SR, Mellersh CS (2007). L-2-hydroxyglutaric aciduria: characterisation of the molecular defect in a spontaneous canine model. J Med Genet 44(5):334-340.
• Abramson CJ, Platt SR, Jakobs C, Verhoeven NM, Dennis R, Garosi L, Shelton GD (2003). L-2-Hydroxyglutaric aciduria in Staffordshire Bull Terriers. J Vet Intern Med 17(4):551-556.
• Abramson C, Garosi L, Platt S, Penderis J (2001). Metabolic defect in Staffordshire bull terriers. Vet Rec 149(17):532.
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• Böhm M, Henderson H, Van der Zwan H, Basson S (2014). L-2 hydroxyglutaric aciduria in a South African Staffordshire Bull Terrier. J S Afr Vet Assoc 85(1):1042.
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• Christen M, Janzen N, Fraser A, Sewell AC, Jagannathan V, Guevar J, Leeb T, Sanchez-Masian D (2021). L2HGDH Missense Variant in a Cat with L-2-Hydroxyglutaric Aciduria. Genes (Basel) 12(5):682.
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• Collins D, Angles JM, Christodoulou J, Spielman D, Lindsay SA, Boyd J, Krockenberger MB (2013). Severe subacute necrotizing encephalopathy (Leigh-like syndrome) in American Staffordshire bull terrier dogs. J Comp Pathol 148(4):345-353.
• Donner J, Freyer J, Davison S, Anderson H, Blades M, Honkanen L, Inman L, Brookhart-Knox CA, Louviere A, Forman OP, Chodroff Foran R (2023). Genetic prevalence and clinical relevance of canine Mendelian disease variants in over one million dogs. PLoS Genet 19(2):e1010651.
• Rzem R, Veiga-da-Cunha M, Noël G, Goffette S, Nassogne MC, Tabarki B, Schöller C, Marquardt T, Vikkula M, Van Schaftingen E (2004). A gene encoding a putative FAD-dependent L-2-hydroxyglutarate dehydrogenase is mutated in L-2-hydroxyglutaric aciduria. Proc Natl Acad Sci U S A 101(48):16849-16854.
• Topçu M, Jobard F, Halliez S, Coskun T, Yalçinkayal C, Gerceker FO, Wanders RJ, Prud’homme JF, Lathrop M, Ozguc M, Fischer J (2004). L-2-Hydroxyglutaric aciduria: identification of a mutant gene C14orf160, localized on chromosome 14q22.1. Hum Mol Genet 13(22):2803-2811.
• Rzem R, Vincent MF, Van Schaftingen E, Veiga-da-Cunha M (2007). L-2-hydroxyglutaric aciduria, a defect of metabolite repair. J Inherit Metab Dis 30(5):681-689.
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• Nicholas FW, Tammen I, Sydney Informatics Hub. OMIA:001371-9615: L-2-hydroxyglutaricacidemia in Canis lupus familiaris (dog). Online Mendelian Inheritance in Animals, University of Sydney. Accessed 2026-10-16.

About the author

Elena Marsh

Editor & writer (not a veterinarian)

A writer with a molecular-biology background and a lifelong dog and cat owner. Not a veterinarian — she translates peer-reviewed genetics research and primary data into plain language, always as information rather than diagnosis.