Who May Benefit from the FRAT® Test

FRAT^® serves as a biomarker test designed to identify a very specific immune-mediated problem — folate receptor alpha autoantibodies that can block the transport of folate into the brain, even when blood folate levels appear perfectly normal. The individuals most likely to benefit are those with clinical presentations consistent with “cerebral folate deficiency” despite normal serum folate, and those for whom identifying this mechanism could meaningfully alter treatment decisions.

The FRAT^® test (Folate Receptor Autoantibody Test)
detects and quantifies autoantibodies directed against folate receptor alpha (FRα), a high-affinity membrane protein responsible for transporting 5-methyltetrahydrofolate (5-MTHF) — the active form of folate — across the blood-brain barrier and into the cerebrospinal fluid.

The test differentiates between two types of autoantibodies:

• Blocking antibodies: directly interfere with folate binding to the receptor
• Binding antibodies: attach to the receptor without necessarily blocking its function directly.

This distinction matters. Blocking antibodies are the ones most clearly implicated in cerebral folate deficiency — they prevent 5-MTHF from reaching the brain. Binding antibody titers, however, have also been shown to correlate with treatment response in some populations.

Developed by Dr. Edward V. Quadros at SUNY Downstate, FRAT® is designed as a blood test that can serve as a less invasive screening tool, potentially replacing the need for lumbar puncture as an initial step in evaluation.

Before identifying who should be tested, it helps to understand the condition FRAT^® is designed to detect.

Cerebral folate deficiency is defined by low cerebrospinal fluid 5-MTHF despite normal serum folate levels.This paradox — adequate folate in the blood but insufficient folate in the brain — is the hallmark of the condition. The symptoms can be devastating: developmental delay, speech impairment, motor dysfunction, seizures, and features overlapping with autism spectrum disorder.

In the landmark 2005 study published in the New England Journal of Medicine, Ramaekers and colleagues found that 25 of 28 children (89%) with cerebral folate deficiency had high-affinity blocking folate receptor autoantibodies,while none of the 28 control subjects tested positive. Oral folinic acid normalized CSF 5-MTHF levels and led to clinical improvement.

This is the most well-established population. FRAT® testing may be warranted in infants and young children presenting with:

• Developmental delay (particularly affecting speech, learning, or behavior)
• Abnormal muscle tone (hypotonia or ataxia)
• Motor dysfunction or movement disorders
• Seizures (especially treatment-resistant)
• Decelerating head growth
• Severe sleep disturbances and irritability

The clinical picture often emerges between 4 and 6 months of age. Early detection matters because folinic acid treatment has been shown to normalize CSF folate levels and produce clinical improvement.

Not every child with ASD needs FRAT^® testing. But a substantial subgroup may benefit.

Research from Dr. Quadros and collaborators found that approximately 70% of children with autism spectrum disorder tested positive for folate receptor autoantibodies.In a 2008 study of 25 children with early-onset low-functioning autism with or without neurological deficits,23 of 25 had low CSF 5-MTHF despite normal serum folate, and
19 of these cases could be explained by serum folate receptor autoantibodies.

A 2024 retrospective analysis of 110 ASD patients found that higher binding FRAA titers were associated with greater response to leucovorin (folinic acid) treatment, with improvements in social responsiveness and irritability.

Signals that might warrant testing in ASD include:

• Developmental regression (especially after a period of typical development)
• Associated neurological deficits (seizures, movement abnormalities)
• Severe gastrointestinal symptoms (some research suggests higher FRAA prevalence in this subgroup)
• Limited response to standard nutritional approaches
• Family history of autoimmune conditions

A critical caveat: FRAT is not a diagnostic test for autism and does not replace a comprehensive ASD assessment. It identifies a potentially treatable biological subgroup within a heterogeneous condition.

The FRAT^® story has deep roots in reproductive medicine.

In 2004, Rothenberg and colleagues published findings in the New England Journal of Medicine showing that 9 of 12 women with a current or previous pregnancy affected by neural tube defects had autoantibodies against folate receptors,compared to only 2 of 20 control women. These antibodies blocked folate binding and cellular uptake.

A subsequent study in a Chinese population confirmed a dose-response relationship between maternal plasma FR autoantibody levels and neural tube defect risk. Women in the highest tertile of IgG autoantibodies had a 5.53-fold increased odds of having an NTD-affected pregnancy.

The clinical implication is significant: some neural tube defects may occur despite adequate folic acid supplementation because autoantibodies prevent folate from reaching the developing fetus. For women with a history of NTD-affected pregnancy — or unexplained recurrent pregnancy complications — FRAA evaluation may provide a previously overlooked explanation.

A study of patients with schizophrenia unresponsive to conventional treatment found that 15 of 18 patients (83.3%) had positive serum FR autoantibodies, compared to only 1 in 30 controls (3.3%). Antibody titers fluctuated over time, correlating with CSF folate levels. In seven patients treated with folinic acid for at least six months, clinical improvement was observed.

The authors recommended that assessment of FR autoantibodies in serum be considered for schizophrenic patients, particularly those who do not respond adequately to standard treatment.

Rett syndrome has been associated with low CSF 5-MTHF in a subset of patients. A European study found that 14 of 33 Rett patients (42%) had low CSF folate levels despite normal plasma folate, and blocking FR autoantibodies were found in 8 patients (24%), six of whom had low CSF folate.

The incidence was notably higher in North-Western Europe compared to North America, where food folate fortification may provide protective effects. FRAT^® testing may be considered in Rett syndrome patients with neurological deterioration that exceeds what would be expected from the underlying genetic condition alone.

FRAT^® may also be relevant for adults presenting with:

• Treatment-resistant depression or mood disorders
• Unexplained neurological symptoms (cognitive decline, movement abnormalities)
• Autoimmune conditions with neuropsychiatric features

Case reports describe individuals whose lives were transformed by identifying FRAA positivity after years of ineffective psychiatric treatment. While large-scale studies in adult psychiatric populations are more limited, the mechanism is biologically plausible and the test is low-risk.

Understanding the limitations is as important as knowing who to test.

A positive FRAT^® does not confirm cerebral folate deficiency. The gold standard remains lumbar puncture with CSF 5-MTHF measurement. FRAT^® identifies a mechanism (autoimmune interference with folate transport) but does not prove that this mechanism is causing a specific patient’s symptoms.

A negative FRAT does not completely rule out CFD. Other mechanisms can impair folate transport, and antibody titers can fluctuate over time. The presence of antibodies alone does not mandate treatment — clinical correlation is essential.

The value of FRAT^® testing lies in its potential to identify individuals who may benefit from reduced folates such as folinic acid (leucovorin) supplementation — a form of folate that can bypass the blocked receptor and enter the brain through alternative transport mechanisms such as the reduced folate carrier.

Multiple studies have demonstrated clinical improvement with folinic acid in FRAA-positive individuals:

• In the original CFD cohort, oral folinic acid normalized CSF 5-MTHF and led to clinical improvement.
• In low-functioning autism with neurological deficits, folinic acid supplements led to normal CSF 5-MTHF and partial or complete clinical recovery after 12 months.
• In a 2024 ASD study, higher binding FRAA titers predicted greater treatment response to leucovorin.
• In treatment-resistant schizophrenia, folinic acid administration resulted in clinical improvement.

The 2025 national attention on leucovorin for autism has brought this research into public view, but the scientific foundation has been building for over two decades.

FRAT^® testing is most appropriate when all three of the following conditions are met:

1. Clinical suspicion: The individual has symptoms consistent with cerebral folate deficiency (developmental delay, regression, seizures, movement disorders, treatment-resistant neuropsychiatric symptoms)
2. Normal serum folate: Routine blood work shows adequate folate levels, creating a paradox with clinical presentation
3. Potential treatment implications: Identification of FRAA positivity would meaningfully alter management (e.g., consideration of reduced folate/folinic acid therapy and dietary adjustments such as a dairy free diet)

Testing is not indicated for:

• Individuals without clinical symptoms suggestive of folate transport impairment
• As a substitute for comprehensive diagnostic evaluation of autism or other neurodevelopmental conditions

It is important to acknowledge that FRAT^® testing and reduced folate/ folinic acid treatment for FRAA-positive individuals remain areas of active investigation. A 2026 federal strategic planning document emphasized the need for assay harmonization, biomarker-defined clinical trials, and validated evidence before broad clinical or coverage recommendations can be made.

The evidence base is strongest for:

• Infantile-onset cerebral folate deficiency
• FRAA-positive ASD with neurological deficits
• Neural tube defect risk in FRAA-positive women

For other populations, the evidence is suggestive but less robust. Research, however, is increasing.

The FRAT^® test addresses a fundamental question that traditional blood tests cannot answer: Is folate actually reaching the brain?

For decades, patients with neurological deterioration and normal blood work fell through the cracks of conventional medicine. The discovery of folate receptor autoantibodies and the development of the FRAT^® test represent a paradigm shift — from measuring what is in the blood to assessing whether it can get where it needs to go.

The individuals most likely to benefit are those whose clinical picture suggests a “starving brain” despite a well-nourished bloodstream. For these patients, FRAT^® testing may open a door to targeted treatment that addresses the underlying mechanism rather than just the symptoms.

As with any specialized medical test, the decision to pursue FRAT^® testing needs to be made in consultation with a qualified healthcare provider who can interpret results in the context of the full clinical picture and guide appropriate next steps.

1. https://pubmed.ncbi.nlm.nih.gov/14711912/#1
2. Levels of folate receptor autoantibodies in maternal and cord blood and risk of neural tube defects in a Chinese population.
   Yang, Na; Wang, Linlin; Finnell, Richard H; Li, Zhiwen; Jin, Lei; Zhang, Le; Cabrera, Robert M; Ye, Rongwei; Ren, Aiguo.
3. Birth Defects Res A Clin Mol Teratol ; 106(8): 685-95, 2016 Aug.
   Article em En | MEDLINE | ID: mdl-27166990
4. https://www.sciencedirect.com/science/article/abs/pii/S1096719214003114
5. https://orbi.uliege.be/bitstream/2268/168813/1/Folate%20receptor%20autoantibodies%20and%20spinal%20fluid%205-methyltetrahydrofolate%20deficiency%20in%20Rett%20syndrome.pdf

6. https://www.downstate.edu/about/office-of-the-president/presidents-bulletin/2025/10-07/04-research-on-folate-and-autism.html#1
7. https://iacc.hhs.gov/meetings/iacc-meetings/2026/full-committee-meeting/july/IACC%20Strategic%20Plan%20Working%20Draft%20July%2017.pdf#46#13
8. https://orbi.uliege.be/bitstream/2268/168811/1/Folate%20receptor%20autoimmunity%20and%20cerebral%20folate%20deficiency%20in%20low-functioning%20autism%20with%20neurological%20deficits.pdf