GSD Type XII • ALD-A Deficiency • Aldolase A Deficiency

Extremely rare. Not HFI. Different enzyme, different tissues, different consequences.

If you searched for HFI and landed here — read this first

Hereditary fructose intolerance and Aldolase A deficiency are both enzyme deficiencies in the aldolase family. That is where the similarity ends.

HFI is caused by a deficiency of Aldolase B — the enzyme form found in the liver, kidneys, and small intestine. It is a fructose metabolism disorder. The problem is fructose. The consequences are hepatic, renal, and systemic.

Aldolase A deficiency is caused by a deficiency of Aldolase A — the enzyme form found in muscle tissue and red blood cells. It has nothing to do with fructose. It does not cause liver damage. The dietary trigger is not fructose — it is exertion, fever, or illness triggering muscle breakdown.

If you are looking for information on hereditary fructose intolerance, the HFI page is in the Metabolic & Genetic section of the Medical Library. You are in a different room.

What it is

Aldolase A deficiency — formally classified as Glycogen Storage Disease Type XII — is an extremely rare inherited metabolic disorder caused by mutations in the ALDOA gene. The gene encodes the aldolase A enzyme, which plays a critical role in glycolysis — the process by which cells break down glucose for energy.

Aldolase A is the dominant form of aldolase in muscle tissue and red blood cells. When it is deficient or dysfunctional, two systems take the hit: skeletal muscle and the red blood cells.

There are fewer than 30 cases formally documented in the medical literature as of the time this page was written. This is not a condition with robust clinical trial data. Most of what is known comes from case reports and small series.

What it is not

Aldolase A deficiency is not:

• Hereditary fructose intolerance (HFI) — that is an Aldolase B deficiency affecting the liver. Different enzyme. Different gene. Different tissues. Different problem.

• A fructose intolerance — dietary fructose is not the trigger and fructose restriction is not the management strategy.

• A condition that primarily affects the liver — Aldolase A is not the dominant aldolase form in the liver. Aldolase B is.

• A common missed diagnosis — it is genuinely rare, not a common condition rarely diagnosed. This is one of the few entries in this library where that distinction matters.

Symptoms

Because Aldolase A is the primary glycolytic aldolase in muscle tissue and red blood cells, the clinical picture involves both systems.

Muscle involvement:

• Exercise intolerance — muscle weakness and fatigue disproportionate to exertion level

• Myalgia — muscle pain during or after physical activity

• Rhabdomyolysis — breakdown of muscle tissue, sometimes severe, releasing myoglobin into the bloodstream

• Myoglobinuria — dark or reddish-brown urine during or after episodes, a sign that muscle breakdown products are being cleared through the kidneys

Red blood cell involvement:

• Hemolytic anemia — red blood cells breaking down faster than the body can replace them

• Jaundice — yellowing of skin or eyes from elevated bilirubin

• Fatigue and pallor consistent with anemia

Episodic triggers: Episodes are frequently triggered by febrile illness — fever and infection are among the most documented precipitants. Intense physical exertion can also trigger muscle breakdown episodes. Between episodes, some patients have relatively stable baseline function.

The severity varies significantly from case to case. Some patients have had severe, life-threatening episodes of rhabdomyolysis in early childhood. Others have a milder, more episodic course identified later in life.

History

Aldolase A deficiency has been documented in the medical literature since the 1970s, though the number of confirmed cases remains extremely small. The condition is classified among the glycogen storage diseases — inherited disorders of glycogen metabolism — though its mechanism differs from the more commonly discussed GSD types.

The rarity of the condition means diagnosis is frequently delayed. Hemolytic anemia and exercise-induced muscle breakdown are symptoms shared by a number of other conditions, and without genetic testing and enzyme activity confirmation, Aldolase A deficiency is unlikely to appear near the top of any differential list.

The genetic basis — mutations in the ALDOA gene — has been progressively better characterized as molecular genetic tools have improved. But the case literature remains small, and the natural history of the condition across a full lifespan is not well established.

The testing picture

Because this is a disease of specific enzyme function in specific tissues, testing requires more than standard bloodwork.

What may be found on bloodwork during an episode:

• Elevated creatine kinase (CK) — marker of muscle breakdown

• Elevated lactate dehydrogenase (LDH)

• Elevated bilirubin

• Anemia on CBC — reduced red blood cell count, hemoglobin, hematocrit

• Myoglobinuria on urinalysis if rhabdomyolysis is occurring

Definitive diagnosis:

• Molecular genetic testing of the ALDOA gene — identification of pathogenic variants

• Enzyme activity testing in red blood cells or muscle tissue — direct measurement of aldolase A activity

A normal standard metabolic panel does not rule this out. This is a condition where the diagnosis depends on asking the right question and ordering the right test. A physician who has not encountered this condition before may not think to look for it.

If you are pursuing evaluation for unexplained hemolytic anemia combined with exercise intolerance or episodic muscle breakdown, ask your physician specifically about enzyme activity testing and genetic evaluation of the ALDOA gene.

What you can do about it

There is no cure and no FDA-approved treatment for Aldolase A deficiency.

Management is centered on avoiding the known triggers for acute episodes — primarily febrile illness and intense physical exertion — and monitoring for and responding to acute events when they occur.

During acute episodes: Rhabdomyolysis can cause acute kidney injury due to myoglobin load on the kidneys. Aggressive hydration is the primary acute intervention. Hospital-level management may be required for severe episodes.

Monitoring: Regular follow-up for anemia status and renal function, particularly in individuals with a history of rhabdomyolysis.

Genetic counseling: Aldolase A deficiency is inherited in an autosomal recessive pattern. Both parents carry one copy of the mutated gene. Genetic counseling is appropriate for families with a confirmed diagnosis.

What to avoid:

• Intense exertion during febrile illness — the combination appears to be a significant risk factor for severe episodes

• Situations where early signs of rhabdomyolysis — muscle pain, dark urine — might be missed or delayed in treatment

There is no fructose restriction protocol for this condition. Dietary fructose is not relevant here. Do not conflate with HFI management.

Asking for the right test

If you or someone you care for has unexplained hemolytic anemia combined with exercise intolerance, episodic muscle pain, or a history of rhabdomyolysis — particularly with onset in childhood triggered by illness or exertion — ask your physician specifically about:

• CBC with differential and reticulocyte count

• Creatine kinase (CK) during and between episodes

• Lactate dehydrogenase (LDH)

• Urinalysis for myoglobinuria during symptomatic periods

• Red blood cell aldolase A enzyme activity

• Genetic testing of the ALDOA gene

A normal result on standard bloodwork between episodes does not rule out Aldolase A deficiency. The most informative testing happens during or shortly after an acute episode.

Personal note

Aldolase A deficiency is not part of my personal diagnosis history. I am documenting it here because it sits in the same enzyme family as Aldolase B — the enzyme that causes HFI — and because the confusion between the two is a real problem for people trying to make sense of their own labwork and research.

If you found this page while looking for HFI information, you are not wrong to be looking. The conditions share a family name and nothing else. The liver problems, the fructose sensitivity, the reactive hypoglycemia, the triglyceride connection — those are Aldolase B. If that picture fits you, the HFI page is where you need to be.

If the picture that brought you here is muscle breakdown episodes, dark urine after illness or exertion, and unexplained anemia — you may be in the right room. Push your physician to test the right enzyme in the right tissue at the right time.

I'm not a doctor. I'm not telling you to change your medication.

Sources

• Esposito G, et al. (2004) — Aldolase A deficiency: studies on the biochemical and structural effects of the Glu206Lys mutation. Journal of Inherited Metabolic Disease. — PubMed

• Kreuder J, et al. (1996) — Brief report: inherited metabolic myopathy and hemolysis due to a mutation in aldolase A. New England Journal of Medicine. PMID: 8592468 — PubMed

• Yao DC, et al. (2004) — Hemolytic anemia and severe rhabdomyolysis caused by compound heterozygous mutations of the gene for erythrocyte/muscle isozyme of aldolase, ALDOA. Blood. PMID: 14754868 — PubMed

• Online Mendelian Inheritance in Man (OMIM) — Aldolase A Deficiency, #611881 — omim.org

• Glycogen Storage Disease Type XII — National Organization for Rare Disorders (NORD) — rarediseases.org

• NIH National Center for Advancing Translational Sciences — Genetic and Rare Diseases Information Center (GARD) — rarediseases.info.nih.gov