Phosphofructokinase (PFK-M) Deficiency in English Springer Spaniels (PFKM): What the Research Actually Shows

The English Springer Spaniel is the anchor breed in which canine muscle-type phosphofructokinase (PFK-M) deficiency, also called glycogen storage disease VII (OMIA:000421-9615), was first molecularly defined. It is inherited in an autosomal recessive pattern, so carriers are perfectly healthy and cannot be spotted without a DNA test — only dogs with two copies are affected. Most affected Springers can live near-normal lives if overexertion, excitement, and heat are avoided, but the hemolytic crises this disease can trigger are genuine medical emergencies. A DNA test tells you the genetic risk for breeding and awareness; it is not a clinical diagnosis.

What PFK-M deficiency is, and why the Springer is its namesake breed

SamMy vet mentioned “PFK deficiency” in Springers — what actually is it?

Elena MarshIt’s an inherited enzyme defect. Smith and colleagues in 1996 (PMID 8702726) mapped the exact mutation in the English Springer Spaniel, which is why it’s the reference breed in OMIA.

Muscle-type phosphofructokinase (M-PFK), encoded by the PFKM gene, is one of the key enzymes of glycolysis — the pathway cells use to break down sugar for energy. When a dog inherits two faulty copies of PFKM, it cannot make functional M-PFK, and the resulting condition is known as phosphofructokinase deficiency or glycogen storage disease type VII.

The English Springer Spaniel holds a special place in this story. It was in this breed that Smith BF and colleagues, publishing in the Journal of Biological Chemistry in 1996, identified the causal DNA change: a nonsense mutation designated c.2228G>A, p.(Trp743*). This single letter change introduces a premature “stop” signal that lops off roughly the last 40 amino acids of the M-PFK protein, leaving an unstable product that the body quickly degrades. Because this was the founding molecular description, the Springer is the breed anchored to OMIA:000421-9615 as the canonical example of the disease.

The two-tissue mechanism: hemolytic crises plus exertional myopathy

SamWhy does one enzyme problem affect both blood and muscle?

Elena MarshBecause M-PFK is rate-limiting in glycolysis in both tissues. The 1996 work showed red cells are especially vulnerable — they become alkaline-fragile and rupture under stress.

M-PFK is the rate-limiting (bottleneck) enzyme of glycolysis, so losing it hits any tissue that leans heavily on this pathway. Two axes matter most in dogs.

Red blood cells. PFK-deficient red cells are abnormally alkaline-fragile. When a dog gets excited, exercises hard, or overheats, it hyperventilates; hyperventilation drives off carbon dioxide and produces a respiratory alkalosis — a rise in blood pH. In these dogs, that alkaline shift can trigger an acute intravascular hemolytic crisis: red cells burst inside the bloodstream, releasing hemoglobin that spills into the urine (hemoglobinuria/pigmenturia, so the urine turns dark red-brown). Owners may see pallor, weakness, fever, and jaundice. Between these episodes, affected dogs typically carry a persistent, low-grade compensated hemolysis — the bone marrow works overtime, which shows up as reticulocytosis (increased young red cells) on bloodwork.

Muscle. The same enzyme gap can produce an exertional myopathy: exercise intolerance, a mild rise in creatine kinase (CK) after activity, and in some dogs muscle wasting (atrophy) over time. The muscle signs are usually milder and less dramatic than the blood crises, but they are part of the same underlying defect.

Honest severity: manageable, but crises are real emergencies

SamIs this a death sentence, or something we can live with?

Elena MarshNeither extreme. Per OMIA and PennGen’s testing programs, many affected dogs live near-normal lifespans with careful management — yet a full hemolytic crisis is a genuine emergency.

Here is the balanced truth, and it is important not to slide toward either false alarm or false reassurance. There is no cure for PFK-M deficiency. However, lifestyle management genuinely works, and many affected dogs live near-normal lifespans. The core of management is avoiding the triggers that provoke a crisis: overexertion, high excitement, heat, and prolonged barking or panting. Keeping an affected dog cool, calm, and moderately exercised removes most of the risk.

At the same time, a hemolytic crisis is a real medical emergency. Severe anemia during a crisis may require urgent veterinary care and sometimes a blood transfusion, and hyperthermia (overheating) can be life-threatening on its own. If you own an affected dog and see very dark urine, sudden weakness, pale gums, or collapse, treat it as an emergency and contact your veterinarian immediately. Management lowers risk; it does not make the disease harmless.

Inheritance, carriers, and what the ~14% / ~6% screening figures mean

SamBoth my dog’s parents seemed healthy — how could this be inherited?

Elena MarshIt’s autosomal recessive, so carriers are clinically normal. A US screening of about 600 Springers by the PennGen/Giger group reported roughly 14% carriers and 6% affected.

PFK-M deficiency is inherited in an autosomal recessive pattern. That means a dog needs two copies of the c.2228G>A variant — one from each parent — to be affected. A dog with a single copy is a carrier (heterozygote): clinically normal, indistinguishable from a non-carrier by appearance or behavior, and identifiable only through a DNA test. Two healthy carrier parents can, on average, produce affected puppies, which is exactly why the disease can appear “out of nowhere” in a litter from two apparently normal dogs.

To put frequency in perspective, a US screening effort of roughly 600 English Springer Spaniels by the Giger group at PennGen reported approximately 14% carriers and 6% affected. Treat these as approximate, published screening figures from a specific sampled population — not a precise, current, or universal prevalence. They do, however, make the point that both the carrier and affected states are common enough in the breed to justify routine testing before breeding.

What the DNA test can and cannot tell you (and the differentials)

SamIf I run the DNA test, does that tell me whether my dog is actually sick?

Elena MarshNo — it detects the c.2228G>A allele Smith 1996 defined, but per PennGen it doesn’t measure current enzyme activity, severity, or crisis frequency.

A DNA test for PFK-M deficiency is definitive for the presence of the c.2228G>A allele. It can be run from a cheek swab or blood at any age, works before any symptoms appear, and returns one of three results: clear (no copies), carrier (one copy), or affected (two copies). That makes it a powerful tool for breeding decisions — pairing a carrier with another carrier risks affected puppies, so the test lets breeders avoid carrier × carrier matings — and for pre-symptomatic awareness in a pet.

What the test does not do is equally important. It does not measure your dog’s current enzyme activity, disease severity, or how often a crisis might occur. A clear result for this specific gene also says nothing about other conditions that can cause exertional collapse or hemolysis. Real clinical status is assessed by a veterinarian through enzyme assays and bloodwork — a genetic test is a risk tool, not a diagnosis.

Finally, several other conditions can mimic parts of this picture and should be considered by your veterinarian: Exercise-Induced Collapse (associated with the DNM1 gene), pyruvate kinase deficiency (PKLR, another glycolytic red-cell enzymopathy), immune-mediated hemolytic anemia (IMHA), heat stroke, and exertional rhabdomyolysis. Because these overlap in signs like collapse, weakness, or dark urine, a definitive answer requires veterinary workup rather than genetics alone.

FAQ: PFK-M deficiency in English Springer Spaniels

Q. Is PFK-M deficiency as dangerous as it sounds?
It is a serious condition, but not usually a hopeless one. Many affected dogs live near-normal lifespans when owners avoid overexertion, excitement, and heat. That said, this is not a mild disease you can ignore: acute hemolytic crises are real emergencies that can cause severe anemia and, with overheating, become life-threatening. The honest summary is “manageable, but demands respect.”

Q. My dog is a carrier. Will it get sick?
No. Because the disease is autosomal recessive, a carrier has only one copy of the c.2228G>A variant and is clinically normal. Carriers do not develop the disease, but they can pass the variant to their puppies, which matters for breeding decisions.

Q. Can a DNA test tell me how severe my affected dog’s disease will be?
No. The DNA test confirms the presence of the c.2228G>A variant, but it does not measure current enzyme activity, predict how often crises will occur, or grade severity. Those questions are answered by a veterinarian using enzyme assays and bloodwork.

Q. My dog collapsed after playing — is it definitely PFK deficiency?
Not necessarily. Several conditions can cause exertional collapse or dark urine, including Exercise-Induced Collapse (DNM1), pyruvate kinase deficiency (PKLR), immune-mediated hemolytic anemia, heat stroke, and exertional rhabdomyolysis. See your veterinarian for a proper diagnosis; a genetic result alone cannot confirm or rule these out.

References and further reading

• Online Mendelian Inheritance in Animals (OMIA) — Phosphofructokinase deficiency, muscle-type in Canis lupus familiaris (OMIA:000421-9615): https://omia.org/OMIA000421/9615/
• Smith BF, Stedman H, Rajpurohit Y, et al. Molecular basis of canine muscle type phosphofructokinase deficiency. J Biol Chem. 1996 (PMID 8702726): https://pubmed.ncbi.nlm.nih.gov/8702726/
• PennGen (University of Pennsylvania) — Phosphofructokinase (PFK) Deficiency genetic testing information: https://netapps.vet.upenn.edu/PennGen/SampleTesting/GeneticsTest.aspx?testid=28
• OMIA variant record — PFKM c.2228G>A, p.(Trp743*) in the dog: https://omia.org/OMIA000421/9615/
• National Center for Biotechnology Information (NCBI) Gene — PFKM phosphofructokinase, muscle: https://www.ncbi.nlm.nih.gov/gene/5213

Eyecatch photo: “’Harvey’ the Springer Spaniel is an Arms Explosive Search (AES) dog, currently serving in Afghanistan MOD 45148184” by Cpl Ian Houlding, OGL 3, via Wikimedia Commons.

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.