FOLR1-related cerebral folate transport deficiency is a rare, treatable neurometabolic disorder caused by biallelic pathogenic variants in FOLR1. The disorder reduces transport of 5-methyltetrahydrofolate into the brain, producing severe cerebral folate deficiency despite normal systemic folate status.
Why it matters in epilepsy
Untreated disease can cause developmental slowing or regression, seizures, movement disorders, progressive cognitive impairment and loss of mobility.
Recognition matters because targeted folate replacement can substantially improve neurological function and can reduce or eliminate seizures in some people.
Typical presentation
Children may initially develop normally and then show developmental plateau or regression, ataxia, movement abnormalities and epilepsy.
Age at onset and severity vary, so the disorder should not be restricted to one narrow childhood presentation.
Seizures
Seizure types are variable and may include focal or generalised seizures.
Some individuals develop drug-resistant epilepsy before the metabolic diagnosis is made.
CSF folate is the key biochemical clue
The characteristic finding is a very low cerebrospinal-fluid concentration of 5-methyltetrahydrofolate.
Blood folate can be normal because the defect involves transport into the central nervous system rather than lack of dietary folate.
Genetics
The condition is autosomal recessive and caused by loss-of-function variants in FOLR1.
Molecular confirmation helps establish the diagnosis and supports family counselling.
Treatment
The targeted treatment is folinic acid, also called 5-formyltetrahydrofolate.
GeneReviews describes this therapy as essential. Seizure frequency may fall markedly, and some people may eventually no longer require antiseizure medicine once adequate cerebral folate replacement is achieved.
Why ordinary folic acid is not the same treatment
Folinic acid and folic acid are not interchangeable in this disorder.
Treatment should be directed by a metabolic specialist because the objective is to restore physiologic cerebral folate concentrations.
Monitoring
Clinical response includes seizure burden, cognition, movement and function.
Specialist follow-up may include repeat CSF folate assessment to ensure adequate replacement.
Medication interactions
Some antiseizure medicines can influence folate metabolism. GeneReviews specifically notes valproate as relevant to one-carbon folate metabolism.
This does not mean valproate is universally contraindicated, but treatment decisions should consider the metabolic disorder.
MRI
Neuroimaging can show white-matter abnormalities, cerebral or cerebellar atrophy and other non-specific changes.
MRI does not replace biochemical and genetic diagnosis.
Outcome
Earlier treatment offers the best opportunity to prevent irreversible neurological deterioration.
People diagnosed after substantial regression may still improve, but recovery may be incomplete.
Worldwide access
The major barriers are recognition, access to lumbar puncture with specialised CSF folate analysis and genomic testing.
Because the disorder is treatable, delayed diagnosis has unusually high consequences.
The central point
Cerebral folate transport deficiency is a treatable cause of epilepsy and neurological regression in which blood folate can be normal. The critical abnormality is deficient folate transport into the brain.
Related reading
Metabolic Epilepsies →
Genetic Testing in Epilepsy →
Sources
Medical note: folinic-acid treatment should be supervised by a specialist metabolic or neurological team.
Evidence checked: September 2026.