Folate Receptor Autoantibodies: Understanding Their Role in Cerebral Folate Transport Research

Folate (vitamin B9) is essential for normal brain function and development. However, having adequate folate in the blood does not always mean enough reaches the brain. Researchers are investigating whether folate receptor alpha autoantibodies (FRAAs) can interfere with this transport process in some individuals. 

What Are Folate Receptor Alpha Autoantibodies? 

Folate receptor alpha (FRα) is a protein that helps transport folate across cell barriers, including the blood–cerebrospinal fluid barrier at the choroid plexus. This process helps maintain adequate levels of 5-methyltetrahydrofolate (5-MTHF), the main active folate form found in cerebrospinal fluid (CSF). 

FRAAs are antibodies produced by the immune system that target FRα. Researchers have identified two types: 

• Blocking antibodies: May interfere with folate binding to its receptor. 
• Binding antibodies: Attach to the receptor, although their functional effect is not necessarily the same as that of blocking antibodies. 

How Are FRAAs Linked to Cerebral Folate Deficiency? 

Cerebral folate deficiency (CFD) refers to low CSF 5-MTHF levels, sometimes despite normal folate levels in the blood. FRAAs are one proposed mechanism that may contribute to impaired folate transport. Genetic conditions involving the FOLR1 gene and other metabolic disorders can also cause CFD. 

Research has reported FRAAs in some individuals with neurological and developmental conditions, including autism. However, these findings do not establish that FRAAs cause autism or that every antibody-positive individual has CFD. 

What Does FRAA Testing Tell You? 

The folate receptor autoantibody test (FRAT) is a specialised blood test that looks for antibodies against FRα. Depending on the assay, it may assess blocking and/or binding antibodies. Yoda Diagnostics would perform the FRAT test for total folate receptor autoantibodies providing a sum of blocking and binding antibodies. 

A positive result indicates antibody detection, not a confirmed neurological diagnosis. Blood testing is not standardised across all laboratories and cannot independently confirm CFD. CSF 5-MTHF measurement, genetic investigations and clinical assessment may be considered by specialists when CFD is suspected. 

For an overview of current clinical limitations, see the American Academy of Pediatrics' guidance on FRAT testing. 

Learn more about FRAT IgG testing to discuss whether testing is appropriate with your healthcare provider and interpret results in the context of the complete clinical picture. 

Frequently asked questions 

What are folate receptor autoantibodies? 

They are antibodies that target folate receptor alpha, a protein involved in transporting folate across cell barriers. Some may interfere with normal folate transport. 

How do folate receptor autoantibodies affect the brain? 

Blocking antibodies may interfere with folate transport into the central nervous system. This may contribute to low CSF folate levels in some individuals, but a positive antibody result does not confirm cerebral folate deficiency. 

What causes cerebral folate deficiency? 

Possible causes include FOLR1 gene variants, folate receptor autoantibodies, mitochondrial disorders and certain metabolic conditions. The cause needs individual clinical investigation. 

How is cerebral folate deficiency diagnosed? 

Assessment may include measuring 5-MTHF in cerebrospinal fluid through lumbar puncture, genetic testing and other investigations guided by a specialist. Blood FRAA testing alone cannot establish the diagnosis. 

Does folic acid worsen folate receptor autoantibodies? 

There is insufficient evidence to conclude that folic acid worsens FRAAs. Supplementation decisions should be based on individual clinical needs and medical advice. 

Why do folate receptor autoantibody levels fluctuate? 

Some studies have reported changes in antibody levels over time. However, the extent and clinical meaning of these changes are not fully established. A result should be interpreted alongside the assay method and clinical findings. 

Where can I get a folate receptor antibody test in India, and what if the result is negative? 

Specialised laboratories in India, including Yoda Diagnostics has FRAT testing. A negative result means the antibodies measured were not detected in that sample; it does not rule out every cause of impaired cerebral folate transport. Discuss further evaluation with a healthcare professional if clinically indicated. 

References 

• Autoantibodies to folate receptors in the cerebral folate deficiency syndrome. N Engl J Med. 2005.  
• Cerebral folate deficiency. Dev Med Child Neurol. 2004. 
• Clinical recognition and aspects of the cerebral folate deficiency syndromes. Clin Chem Lab Med. 2013.  
• Rossignol DA, Frye RE. Cerebral folate deficiency, folate receptor alpha autoantibodies and leucovorin (folinic acid) treatment in autism spectrum disorders: a systematic review and meta-analysis. J Pers Med. 2021.  
• FOLR1-Related Cerebral Folate Transport Deficiency. In: GeneReviews®. University of Washington, Seattle.