Organic acidemias are inherited metabolic disorders in which toxic organic acids or related metabolites accumulate. Important examples include propionic acidemia, methylmalonic acidemia and several other disorders of amino-acid and intermediary metabolism.
Seizures may occur during acute metabolic decompensation, as a consequence of previous brain injury, or as chronic epilepsy.
Why seizures occur
Metabolic acidosis, hyperammonaemia, hypoglycaemia, mitochondrial dysfunction and toxic metabolite accumulation can all disturb brain function.
Basal-ganglia and cortical injury during crises can later create persistent seizure susceptibility.
Propionic acidemia
Propionic acidemia is caused by deficiency of propionyl-CoA carboxylase.
Neonatal disease can present with feeding difficulty, lethargy, metabolic acidosis, hyperammonaemia, seizures and coma.
Methylmalonic acidemia
Methylmalonic acidemia can result from defects in methylmalonyl-CoA mutase or cobalamin metabolism.
Neurological complications include developmental impairment, movement disorders, metabolic stroke and seizures.
Seizures during crisis
Acute seizures can occur when metabolic control deteriorates during infection, fasting, surgery or other catabolic stress.
In this setting, correcting the metabolic crisis is as important as giving antiseizure treatment.
Chronic epilepsy
Some people continue to have epilepsy between metabolic crises because of established brain injury or ongoing metabolic vulnerability.
Seizure type varies widely.
EEG
EEG abnormalities can include diffuse slowing, focal epileptiform discharges and generalised abnormalities.
EEG findings are not specific to one organic acidemia.
MRI
Basal-ganglia injury is a recognised feature of several organic acidemias.
White-matter abnormalities, cerebral atrophy and other injury patterns may also occur.
Diagnosis
Testing may include blood gas, glucose, ammonia, lactate, plasma amino acids, acylcarnitine profile and urine organic acids.
Molecular testing confirms the specific disorder.
Acute metabolic management
Treatment generally aims to reverse catabolism, provide adequate calories, reduce toxic precursor load and correct acidosis or hyperammonaemia.
Specific regimens depend on the disorder.
Dietary treatment
Many organic acidemias require carefully controlled protein or precursor intake.
Over-restriction can itself cause malnutrition, so management requires an experienced metabolic dietetic team.
Cofactor-responsive disease
Some disorders respond to vitamin or cofactor therapy, including selected cobalamin-responsive methylmalonic acidemias.
Identifying the exact biochemical defect therefore matters.
Antiseizure treatment
Medication choice should account for liver, renal and metabolic status.
No single antiseizure medicine is appropriate for all organic acidemias.
Long-term complications
Cardiomyopathy, kidney disease, pancreatitis, hearing impairment, movement disorders and cognitive disability can occur depending on the specific disorder.
Worldwide access
Expanded newborn screening identifies some organic acidemias before symptoms, but coverage differs greatly between countries.
Where screening is absent, epilepsy may be one of the first clues to an underlying metabolic disease.
The central point
Seizures in organic acidemias may be a symptom of an active metabolic crisis rather than an isolated epilepsy problem. The biochemical emergency and the seizure both need treatment.
Related reading
Sources
Medical note: acute metabolic decompensation with seizures requires urgent specialist assessment.
Evidence checked: September 2026.