Leucovorin (Folinic Acid) and Autism Treatment Potential

When a new treatment for autism emerges, it is a cause for cautious celebration. The prevalence of autism has risen precipitously and is now estimated at approximately 1 in 31 children. Autism is a complex, heterogeneous condition without simple answers. Despite a shared diagnostic label, there is clinically significant biological diversity that drives a wide range of symptoms and responses to treatment.

This diversity is essential to keep in mind when discussing Leucovorin. While there are reasons for optimism based on current research and clinical experience, it is equally important to understand the specific conditions for which Leucovorin may be beneficial, so that expectations remain informed and realistic.

In the fall of 2005, the FDA announced that it was seeking approval for the use of Leucovorin in children with cerebral folate deficiency (CFD), a condition that is often present in individuals with autism. Depending on the study and the methodology used, the prevalence of CFD in autism is estimated to range from 38% to 44%. Screening for folate receptor alpha (FRα) antibodies—which can lead to CFD—reveals an even higher prevalence, with estimates ranging from 58% to 76% in individuals with autism. Regardless of the exact percentage, there is sufficient evidence to justify serious attention to this therapeutic approach and a careful understanding of the underlying science.

The Folate Receptor alpha and Cerebral Folate Deficiency

Folate is essential for DNA synthesis and repair, red blood cell formation, cell division and growth, protein synthesis, and the production and regulation of neurotransmitters. Folate enters cells in the body through the folate receptor alpha. In tissues outside the brain, folate and folinic acid can be transported into cells directly.  In the brain, however, the active, methylated form of folate is required to pass through the blood–brain barrier via the folate receptor alpha.

When antibodies against the folate receptor alpha are present, folate transport is impaired throughout the body but is most clinically significant in the brain when considering autism or other developmental delays. In this context, the condition is referred to as cerebral folate deficiency. As will be discussed below, Leucovorin is unique in that it can enter the brain through an alternate transport pathway that is not affected by these folate receptor antibodies.

Types of Folate (Vitamin B9)

There are several forms of folate, and understanding the distinctions between them is clinically important when considering the role of Leucovorin:

Natural folate

This is the form of vitamin B9 found in foods. It must be converted into its active, methylated form in order to cross the blood–brain barrier and be used by brain cells.

Folic acid

This is the synthetic form of folate found in many vitamin supplements and fortified foods. It must be converted into the active form before it can be used by the body and the brain. Under normal conditions, the body performs this conversion through several enzymatic steps, including the addition of a methyl group. However, genetic variations—most notably polymorphisms in the MTHFR gene—can impair this process, resulting in reduced availability of active folate in the brain.

Methylfolate

This is the active form of folate. It is naturally produced in the body or provided in supplement form for individuals with impaired methylation, most commonly due to variants of the MTHFR gene.

Folinic acid

This is a naturally occurring form of folate found in small amounts in food and produced in the body. It is also available in synthetic form in supplements and as the prescription medication Leucovorin. Folinic acid is unique in that it can bypass the folate receptor alpha, the primary transport mechanism for folate into the brain, and it does not require conversion by the DHFR enzyme, which is a necessary step in the activation of folic acid.

What makes Leucovorin unique?

Leucovorin is the pharmaceutical form of folinic acid. It is able to enter the brain through the reduced folate carrier, bypassing the primary transport system that depends on the folate receptor alpha. In individuals with antibodies to the folate receptor alpha, transport of methylfolate into the brain is impaired. Leucovorin, however, is able to utilize this alternate “back door” pathway.

Although folinic acid still requires methylation once inside the brain in order to become fully active, it bypasses the DHFR-dependent step in the activation pathway. The final conversion may still be impaired in individuals with significant reductions in MTHFR enzyme activity, and these patients may benefit from additional methylfolate supplementation.

However, some studies suggest that Leucovorin may be particularly beneficial in individuals who have both folate receptor alpha antibodies and MTHFR polymorphisms. Whether additional methyl B folate is required is based on the clinical outcome of Leucovorin by itself but there is no contraindication to giving both folinic acid and methyl B folate.

Clinical Research Evidence for Leucovorin Use in Autism

The strongest evidence comes from two double blind randomized placebo controlled studies which studied the effect of Leucovorin in children with autism. Both studies used the same dose of Leucovorin 2 mg/kg/day to a maximum of 50 mg. Both studies also evaluated outcomes related to presence or absence of folate receptor antibodies.

Forty eight children with autism and language impairment completed 12 weeks of Leucovorin or placebo treatment. Leucovorin resulted in improvement in verbal communication, subscales of the Vineland Adaptive Behavior Scale, the Aberrant Behavior Checklist, the Autism Symptom Questionnaire and the Behavioral Assessment System compared to the placebo group.  Children positive for the folate receptor antibody had the most significant improvement.¹

Seventy seven children aged 2-10 years with autism completed 24 weeks of Leucovorin or  placebo treatment. They found significant changes in the Childhood Autism Rating Scale (CARS) and the Child Behavior Checklist (CBCL) in the Leucovorin group. They concluded that oral folinic acid supplementation is effective and safe in improving ASD symptoms, with more pronounced benefits in children with high titers of folate receptor autoantibodies.²

An open label study by Frye in children with autism and positive folate receptor antibodies showed significantly higher improvement ratings over a mean period of 4 months in verbal communication, receptive and expressive language, attention, and stereotypical behavior. Approximately one-third of treated children demonstrated “moderate to much” improvement.³

A metaanalysis by Rossignol and Frye (2021) found “  Children with ASD were 19.03-fold more likely to be positive for a FRAA compared to typically developing children.  For individuals with ASD and CFD, meta-analysis also found improvements with d,l-leucovorin in overall ASD symptoms.  Significant adverse effects across studies were generally mild. Leucovorin was found to significantly improve communication with medium-to-large effect sizes. Taken together, d,l-leucovorin is associated with improvements in core and associated symptoms of ASD and appears safe and generally well-tolerated, with the strongest evidence coming from the blinded, placebo-controlled studies.⁴

The Bottom Line about Leucovorin for Autism

Given what is known to date, Leucovorin may be especially helpful for children with:

• Autism and language delay
• A diagnosis of cerebral folate deficiency
• Positive folate receptor alpha antibodies
• Certain folate or methylation-related genetic variants (like MTHFR)

Two randomized placebo controlled studies, several open label studies, and clinical reports show improvements in:

• Language and communication
• Attention
• Social interaction
• Behavior
• Overall engagement and learning

Although the role of Leucovorin in autism -particularly in children with positive folate receptor antibodies is promising, more research is warranted and to date major medical organizations such as the American Academy of Pediatrics has not endorsed Leucovorin as a treatment for autism.

So should we be using Leucovorin in children with autism? That of course will vary amongst clinicians and parents but given the fact that Leucovorin was not found to have adverse effects in the research studies to date, it is not unreasonable to consider its use off-label particularly for a child with known folate receptor antibodies.