Exploring the Familial Connection of Folate Receptor Autoantibodies

Folate is an essential nutrient for normal neurodevelopment. It is required for DNA synthesis, methylation, and the production of neurotransmitters. The FRα protein, encoded by the FOLR1 gene, is the primary transporter that ushers folate from the bloodstream into the cerebrospinal fluid and the brain. It also plays a vital role in moving folate from the mother to the fetus during pregnancy.

FRAAs are autoantibodies—antibodies produced by the immune system that mistakenly target the body’s own proteins. When FRAAs bind to FRα, they can block its function. There are two main types of FRAAs:

• Blocking antibodies: These prevent folate from binding to the receptor.
• Binding antibodies: These attach to the receptor and may lead to its degradation or immune-mediated damage.

The presence of these antibodies can result in cerebral folate deficiency (CFD), a neurological condition characterized by low levels of folate in the cerebrospinal fluid despite normal serum folate. CFD has been linked to a range of neurodevelopmental and psychiatric symptoms, including developmental delays, seizures, and autism spectrum disorder.

The first major clue that FRAAs might have a familial component came from studies examining children with autism spectrum disorder and their family members. A landmark 2018 study by Edward Quadros and colleagues, published in Autism Research, evaluated 82 children with ASD, 53 of their unaffected siblings, 65 fathers, and 70 mothers, alongside 52 unrelated typically developing controls.

The results were, indeed, interesting. Overall, 76% of the affected children, 75% of the unaffected siblings, 69% of fathers, and 59% of mothers were positive for either blocking or binding FRAAs. In contrast, the prevalence in the normal control group was only 29%. This high prevalence across all family members—not just the child with ASD—pointed strongly toward a familial origin. The researchers concluded that “the appearance of these antibodies may have a familial origin but the risk of developing ASD is likely influenced by other mitigating factors since some siblings who had the antibodies were not affected.

This study was pivotal because it demonstrated that FRAAs are not solely a feature of the affected individual but are shared across the family unit. It also raised an important question: if the antibodies are present in unaffected siblings and parents, why does only one child develop ASD? This suggests that FRAAs may be a necessary but not sufficient factor, interacting with other genetic or environmental influences to produce the full clinical picture.

Similar familial patterns have been observed in infantile-onset cerebral folate deficiency. In a genetic assessment of 36 patients from 33 families with CFD, researchers found that three families had two affected siblings each, and parents from four families were first cousins. The study analyzed serum FR autoantibodies and the FOLR1 and FOLR2 genes. Most patients (89%) had serum FR autoantibodies that fluctuated over a 5–6 week period.

Notably, pathogenic FOLR1 gene mutations were absent in these patients, meaning the condition was not caused by a direct genetic defect in the folate receptor itself. Instead, the predominant pathology was the presence of autoantibodies. The clustering of cases within families – including affected siblings and consanguineous parents – strongly suggested a familial genetic component in the pathogenesis of the disorder. The researchers suggested that further research should focus on identifying candidate genes predisposing to FRα-autoimmunity.

This distinction is crucial: the familial connection of FRAAs does not appear to be a simple Mendelian inheritance of a single gene mutation. Rather, it likely involves a complex interplay of genetic susceptibility to autoimmunity, environmental triggers, and possibly epigenetic factors.

The most compelling evidence for a familial connection comes from a 2025 study by Frye and colleagues, published in the International Journal of Molecular Sciences. This study reanalyzed data from the earlier Quadros et al. cohort to specifically investigate the transgenerational transmission and heritability of FRAAs.

The researchers made several key findings:

1. Maternal-Offspring Correlation: Offspring blocking FRAA titers were significantly related to maternal blocking titers. This relationship was particularly driven by multiplex families (families with more than one child with ASD). In fact, 53% of multiplex families demonstrated positivity in both offspring and mother, compared to only 12% of simplex families.

2. Transgenerational Increase (Anticipation): FRAA titers increased across generations. Offspring blocking titers were significantly higher than both maternal and paternal blocking titers. This increase was only seen in multiplex families, suggesting that FRAAs may demonstrate anticipation – a phenomenon where a condition becomes more severe or appears earlier in successive generations.

3. Multiplex Families Have Higher Titers: Multiplex ASD families demonstrated significantly higher blocking FRAA titers compared to simplex families, with a large effect size. This is particularly important because multiplex families are less likely to have an identifiable single-gene cause for ASD, suggesting that non-genetic heritable factors like FRAAs may be playing a significant role.

4. Paternal Influence: Paternal FRAA titers were associated with several measures of offspring behavior and cognitive development. The presence of paternal FRAAs was linked to lower general intelligence, locomotor activity, hearing and speech, hand-eye coordination, and social communication in the child with ASD.

5. Association with Known Risk Factors: Higher FRAA titers were associated with known ASD risk factors, including increased maternal and paternal age at birth and multiple birth pregnancies.

The study concluded of a potential transgenerational transmission of FRAAs and their role in ASD. This supports the notion that heritable non-genetic factors may be important in the etiology of ASD and that FRAAs may demonstrate anticipation (worsening across generations), especially in multiplex families.

The concept of “heritable non-genetic factors” may seem paradoxical, but it is increasingly recognized in the study of complex disorders. While DNA sequence itself is inherited, so too are patterns of gene expression, immune system tendencies, and even the composition of the microbiome. FRAAs appear to fall into this category.

The familial clustering of FRAAs could be explained by several mechanisms:

• Genetic susceptibility to autoimmunity: Certain HLA types or other immune-regulatory genes may predispose families to producing autoantibodies, including FRAAs. The fact that consanguineous parents were overrepresented in some CFD cohorts supports a genetic contribution.
• Epigenetic transmission: Environmental exposures (such as infections, toxins, or nutritional factors) during critical developmental windows could alter the epigenome in ways that are transmitted across generations, influencing immune function and autoantibody production.
• Shared environmental exposures: Families share environments, diets, and lifestyles. If an environmental trigger for FRAA production exists—such as a cross-reactive antigen from an infectious agent—family members might be exposed to it simultaneously.
• Maternal-fetal transfer: During pregnancy, maternal IgG antibodies cross the placenta. If a mother has FRAAs, they could transfer to the fetus, potentially affecting fetal brain development and priming the child’s immune system. The correlation between maternal and offspring blocking titers supports this possibility.

The 2025 Frye et al. study found that the heritability of blocking FRAAs was different from that of binding FRAAs. Blocking titers showed clear transgenerational transmission and correlation between mothers and offspring, while binding titers did not show the same pattern. This suggests that the two types of antibodies may have different etiologies and transmission pathways.

Understanding the familial nature of FRAAs has several important clinical implications.

1. Screening for at-risk families: If a child is diagnosed with ASD and found to have FRAAs, it may be prudent to test family members, especially parents and siblings. This could help identify individuals who might benefit from interventions, even if they are currently asymptomatic.

2. Preconception and pregnancy planning: The high prevalence of FRAAs in parents raises the possibility of preconception screening and supplementation. As the Quadros et al. researchers noted, “the high prevalence of folate receptor autoantibodies in parents raises the possibility of supplementing the parents positive for [the autoantibodies] before pregnancy occurs and the mother throughout the pregnancy with folinic acid to prevent folate deficiency in the fetus.

3. Treatment with folinic acid (leucovorin): Folinic acid is a reduced form of folate that can bypass the blocked FRα transporter and enter the brain via the reduced folate carrier (RFC). Several placebo-controlled trials have demonstrated that folinic acid treatment results in significant improvements in children with ASD who have FRAAs. If FRAAs are familial, then family members with the antibodies – even if unaffected – might also benefit from this intervention.

While the evidence for a familial connection is compelling, several limitations must be acknowledged. The studies to date have relatively small sample sizes, and the multiplex family subgroup is particularly small. Larger, prospective studies are needed to confirm these findings and to better understand the mechanisms of transmission.

Additionally, the exact mechanisms by which FRAAs are transmitted across generations remain unclear. Is it purely genetic susceptibility to autoimmunity? Is there an epigenetic component? Or is it a combination of shared environmental exposures and genetic predisposition? Longitudinal studies that follow families over time, measuring FRAA titers and environmental exposures, will be essential to answer these questions.

Finally, the relationship between FRAAs and other autoimmune conditions should be explored. Many children with ASD and FRAAs also have other autoimmune phenomena, such as thyroid dysfunction. Understanding the broader autoimmune context could shed light on the familial clustering of these antibodies.

The evidence is now robust that folate receptor autoantibodies are not a sporadic, individual-level phenomenon. They cluster in families, correlate between mothers and offspring, increase across generations, and are associated with known familial risk factors for neurodevelopmental disorders. This familial connection suggests that FRAAs represent a heritable, non-genetic factor that may contribute to the etiology of ASD and cerebral folate deficiency syndrome, particularly in multiplex families.

For families affected by these conditions, this research offers both hope and a call to action. Hope, because understanding the familial nature of FRAAs opens the door to targeted screening (via the FRAT® test) and treatment with folinic acid, which has shown promise in improving outcomes. A call to action, because it underscores the importance of considering the whole family—not just the affected child—when evaluating neurodevelopmental disorders.

As research continues to unravel the complex interplay between genes, immunity, and environment, one thing is clear: folate receptor autoantibodies play a part.

1. https://onlinelibrary.wiley.com/doi/abs/10.1002/aur.1934#1
2. https://www.sciencedirect.com/science/article/abs/pii/S1096719218300544#1
3. Transgenerational Effects and Heritability of Folate Receptor Alpha Autoantibodies in Autism Spectrum Disorder

Richard E. Frye ,*, Ira L. Cohen , Jeffrey M. Sequeira , Zoe Hill, Alina Espinoza, W. Ted Brown, Clifford Mevs, Elaine Marchi, Michael Flory, Edmund C. Jenkins, Milen T. Velinov and Edward V. Quadros