Pyruvate Dehydrogenase Complex Deficiency and Epilepsy

Primary pyruvate dehydrogenase complex deficiency — often called PDH deficiency or PDCD — is a group of genetic metabolic disorders that interfere with the brain’s ability to obtain energy from carbohydrate. Epilepsy is common in many forms, but the condition can also affect development, movement, muscle tone, breathing, growth and other organs.

PDCD belongs in both the genetic and metabolic categories of epilepsy. The genetic change disrupts an enzyme system that normally connects glycolysis — the first stage of glucose breakdown — with the mitochondrial pathways that generate much of the cell’s usable energy.

What the pyruvate dehydrogenase complex normally does

When glucose is broken down, one of the main products is pyruvate. The pyruvate dehydrogenase complex converts pyruvate into acetyl-CoA, which can then enter the citric-acid cycle inside mitochondria and contribute to ATP production.

If the complex does not work properly, pyruvate cannot move efficiently into this energy-producing pathway. More pyruvate may instead be converted to lactate, while tissues — especially the energy-hungry brain — can be left with an inadequate energy supply.

Why the brain is especially vulnerable

The brain requires a large and continuous energy supply. Developing neurons are particularly sensitive to disturbances in mitochondrial energy production.

In PDCD, energy failure can disrupt brain development and function. The result can include developmental delay, hypotonia, movement abnormalities, structural brain differences and epilepsy. The exact pattern depends partly on which gene is affected and how much residual enzyme activity remains.

PDCD is not one single genetic disorder

The pyruvate dehydrogenase complex contains several components, and defects in different genes can produce primary PDCD. PDHA1 is the most frequently involved gene, but other recognised causes include variants in PDHB, DLAT, PDHX, PDP1 and DLD.

Different genetic causes can have different inheritance patterns, associated organ involvement and treatment considerations. A precise molecular diagnosis therefore matters.

What can PDCD look like?

The clinical spectrum is broad. GeneReviews describes presentations ranging from severe neonatal disease to milder childhood or adult neurological syndromes. Features can include:

developmental delay or developmental regression
hypotonia or abnormal muscle tone
epilepsy
ataxia or dystonia
microcephaly in some people
lactic acidosis or recurrent metabolic decompensation
abnormal breathing during severe acidosis
structural brain abnormalities or Leigh-syndrome-like MRI changes
worsening during illness, fever or physiological stress

Not every person has all of these features, and a milder presentation does not exclude the diagnosis.

Epilepsy in PDCD

Seizures can occur in infancy or childhood and may be one of several signs of neurological dysfunction. There is no single seizure type that identifies PDCD.

EEG helps characterise the epilepsy, but it cannot establish the metabolic diagnosis on its own. The wider combination of neurological findings, metabolic abnormalities, imaging and genetic testing is more informative.

Lactate and pyruvate

Lactic acidemia is a common clue because pyruvate that cannot be efficiently converted to acetyl-CoA may be diverted towards lactate. Blood lactate and pyruvate measurements can therefore form part of the investigation.

However, lactate is non-specific and can rise for many reasons, including seizures themselves, difficult blood sampling, strenuous activity, infection and other mitochondrial or metabolic disorders. A single raised lactate level does not diagnose PDCD.

MRI findings

Brain MRI can show a variety of abnormalities. Reported findings include abnormalities of the corpus callosum, cerebral atrophy, ventriculomegaly, basal-ganglia or brainstem lesions associated with Leigh syndrome and other developmental changes.

The MRI pattern varies with genotype and severity. Imaging can support the diagnosis and document brain involvement, but molecular and metabolic testing are needed to define the cause.

How the diagnosis is made

Investigation can include blood gas analysis, lactate and pyruvate, glucose and other metabolic tests, EEG, brain MRI and genomic testing. In some settings, specialised enzyme studies may also be used.

Genetic testing has become central because identifying the exact gene can clarify inheritance, prognosis and treatment. Testing may use a targeted panel, exome or genome sequencing depending on the clinical situation and local health system.

Why ketogenic therapy targets the disease mechanism

In PDCD, carbohydrate-derived pyruvate cannot be processed normally through the pyruvate dehydrogenase complex. A ketogenic diet shifts much of the body’s fuel use towards fat and ketone bodies.

Ketone bodies can be converted into acetyl-CoA without first passing through the defective pyruvate dehydrogenase step. This provides an alternative route into mitochondrial energy metabolism.

For that reason, GeneReviews describes ketogenic dietary therapy as a core treatment for primary PDCD. It has been associated with improvement in seizures, ataxia, lactic acidosis and other neurological features in some people.

Ketogenic treatment is highly individualised

There is no single ketogenic ratio that is correct for every person with PDCD. Diet composition, degree of ketosis, protein provision, micronutrient supplementation and monitoring need to be adjusted to age, genotype, clinical severity and treatment response.

Because PDCD can involve metabolic acidosis and other serious complications, therapeutic ketogenic treatment should be supervised by a metabolic physician and specialist dietitian rather than attempted independently.

What about thiamine?

Thiamine, or vitamin B1, is a cofactor for the pyruvate dehydrogenase complex. Some people with particular molecular defects — especially selected PDHA1 variants — may show biochemical or clinical benefit from pharmacological thiamine.

Response is not universal, and treatment decisions depend on the specific genetic and biochemical diagnosis. Ordinary dietary thiamine intake should not be confused with specialist high-dose metabolic treatment.

Acute illness and metabolic decompensation

Illness, fever or other physiological stress can worsen metabolic instability in some people with PDCD. GeneReviews recommends urgent metabolic assessment when decompensation is suspected, including evaluation of acid–base status, lactate, glucose and other relevant biochemical measures.

Families may be given an individual emergency plan describing when to seek urgent care and how the person should be managed during illness. Plans differ according to genotype, usual diet and local metabolic service.

Why “mitochondrial disorder” needs careful wording

The pyruvate dehydrogenase complex functions in mitochondrial energy metabolism, so PDCD is often discussed alongside mitochondrial disease. However, primary PDCD is genetically and biochemically distinct from many disorders caused by pathogenic variants in mitochondrial DNA or nuclear genes that directly affect the respiratory chain.

Keeping those categories clear matters because treatment and medication risks can differ.

Development and long-term outcome

Developmental impairment is common, but severity varies substantially. Earlier diagnosis and disease-directed treatment may improve metabolic stability and neurological outcome, although existing structural brain injury cannot always be reversed.

Long-term care may involve neurology, metabolic medicine, genetics, dietetics, physiotherapy, occupational therapy, speech and language therapy and educational support.

Worldwide access

PDCD is difficult to diagnose without access to metabolic testing, MRI, genomic sequencing and clinicians familiar with rare neurometabolic disease. In many regions those services are concentrated in major centres or may not be routinely available.

Treatment also depends on sustained specialist ketogenic-diet support, reliable laboratory monitoring and access to appropriate foods, formulas and supplements. These requirements can create substantial geographic and financial barriers even after the diagnosis is known.

The central point

PDCD is not simply epilepsy with a raised lactate. It is a disorder of the metabolic bridge between carbohydrate breakdown and mitochondrial energy production. Identifying that mechanism matters because ketogenic therapy can bypass part of the blocked pathway and provide an alternative source of brain energy.

Sources

Medical note: PDCD can cause serious metabolic acidosis and neurological deterioration. Ketogenic therapy, thiamine treatment and acute illness management require specialist metabolic supervision.

Evidence checked: September 2026.