What is the link between Folate, Subfertility, Brain Development, ASD and FRAAs?

It is well known that Folate supplementation reduces the risk of neural tube defects (NTD) in pregnancy. Folate, also known as vitamin B9, is crucial at the moment of conception for several reasons. It plays a vital role in the early development of the neural tube, which later forms the baby’s brain and spinal cord. Sufficient folate intake before and during early pregnancy can significantly reduce the risk of neural tube defects. Folate is also necessary for the synthesis and repair of DNA, as well as for cell division. During conception and early pregnancy, when cells are rapidly multiplying and differentiating, folate is essential for the proper development of the embryo.

Folate crosses into cells using two main transporter mechanisms. Folate Receptor α(FRα) is the main transporter and mediated transport is the primary mechanism due to its high affinity for folate. Using this mechanism, folate binds to the FRα on the apical side of the cell and the receptor undergoes endocytosis and is transported to the basal side of the cell. This process is an active transport mechanism that requires ATP. The Reduced Folate Carrier (RFC) acts as an alternate system to transport folate. However, it is important to note that the RFC is not as efficient at transporting folate as the FRα mechanism primarily due to lower affinity for folate compared with the FRα.

In the absence of systemic folate deficiency, the discovery of autoantibodies to FRα that block the uptake of folate offers one possible mechanism to explain the response to folate in certain neurological disorders such as cerebral folate deficiency and autism spectrum disorders. The association of folate receptor autoantibodies with pregnancy-related complications including CFD syndrome and autism spectrum disorders, and with the response to folate therapy (folinic acid), is highly suggestive of the involvement of these autoantibodies in the disruption of proper function of the folate pathway.

Folate is important for the proper functioning of reproductive tissues, including the ovaries. It is normally transported to the ovaries via the folate receptor (FRα), and in one study targeting women with difficulties in conceiving, approximately thirty percent (30%) had folate receptor autoantibodies [1]. This study and its respective findings demonstrating the presence of folate receptor autoantibodies in these women offers a plausible explanation for their subfertility. Given that this was a small study, additional studies are warranted. Blockage of the folate receptor alpha by folate receptor autoantibodies during the periconception period could alter proper folate bioavailability during the early stages of cell division and embryogenesis. This hypothesis seems to have considerable merit and certainly warrants further investigation.

Paternal folate deficiency is a less studied subject. The association of paternal folate status to reproduction has largely been limited to sperm quality. Folate, as the initial substrate in one-carbon metabolism, is converted into 5-methyltetrahydrofolate in liver prior to distribution to various tissues. Subsequently, 5-methyltetrahydrofolate catalyzed by methionine synthase with vitamin B12 as cofactor provides homocysteine with a methyl group to form methionine and S-adenosyl-methionine (SAM), the universal methyl donor required for methylation of DNA, RNA, proteins, and lipids and their methylation maintenance. Moreover, 5-methyltetrahydrofolate catalyzed by methylenetetrahydrofolate reductase (MTHFR) generates tetrahydrofolate and 5,10- methylenetetrahydrofolate, which are used for purine and thymidylate biosynthesis, respectively [2],[3].

Despite the essential functions of biosynthesis and methylation, the majority of studies have focused on the role of the folate in the normal reproductive function of women. Thus far, the role of folate in male reproduction, particularly spermatogenesis and spermatogenesis-related gene expression, has been rarely investigated. The folate pathway is so important, and inhibited folate transport which may develop due to the presence of folate receptor autoantibodies, may explain some causes of sub-fertility. Again, it may be prudent to investigate if folate receptor autoantibodies are present in the male as well.

Additionally, it has also been hypothesized that paternal folate deficiency influences placental folate transfer, and in turn, may result in unfavorable fetal outcomes similar to that of maternal folate deficiency [4]. With this is mind, screening for folate receptor autoantibodies in males may be warranted.

FRAT^® (Folate Receptor Antibody Test) was developed to determine the presence of folate receptor autoantibodies in serum. The two types of autoantibodies identified by FRAT^® in the serum of patients are blocking antibodies and binding antibodies. The autoantibodies measured by specific assays, and their pathological effects are described as:

1. Blocking Autoantibodies; the functional blocking of folate transport at the receptor level.
2. Binding Autoantibodies; by disrupting the Folate Receptor alpha via an antigen-antibody-mediated functional deficit and an inflammatory response.

These autoantibodies could exert their effect, either by blocking folate transport or potentially by an antibody-mediated immune reaction. In the absence of gross fetal abnormalities, exposure to these autoantibodies during fetal development or in early infancy could disrupt the structural refinement of the brain and cause functional deficits in later life (i.e. Autism). These observations further attest to the importance of folate status during early brain development and to the identification of factors that could disrupt this essential need.

Because folate receptor autoantibodies are associated with various pathologies during fetal and neonatal development and early brain development, timely detection and intervention could prevent or reverse the consequences of exposure to these antibodies. In such cases, it is advised to consult a physician.