rs202720 — FOLH1

FOLH1 — The Intestinal Folate Gate

Before your body can absorb folate from food, it has to be broken down first. Dietary folate arrives primarily as polyglutamated folate¹¹ polyglutamated folate
Folate from food (spinach, lentils, liver) is attached to a chain of glutamate molecules — up to 8 in some foods. This polyglutamate form cannot cross the intestinal wall. — folate molecules with long glutamate tails that cannot cross the intestinal wall intact. FOLH1 (also called GCPII, glutamate carboxypeptidase II) is the enzyme anchored to the intestinal brush border that clips those tails one by one, releasing the absorbable monoglutamate form. Without adequate GCPII activity, a meaningful fraction of the folate in your food passes through unabsorbed.

rs202720 is an intronic variant in FOLH1 located at chromosome 11, position 49,170,799. It does not change the amino acid sequence of the GCPII enzyme, but intronic variants can influence gene expression, mRNA splicing efficiency, or transcript stability. The C allele is common globally — carried by roughly one in three people — with notable variation across ancestries.

The Mechanism

The GCPII enzyme is a type II transmembrane metallopeptidase expressed on the apical surface of jejunal enterocytes²² jejunal enterocytes
Enterocytes are the absorptive cells lining the small intestine, particularly the jejunum, where folate absorption occurs.. It processes dietary polyglutamated folates into the monoglutamate form that the proton-coupled folate transporter (PCFT/SLC46A1)³³ proton-coupled folate transporter (PCFT/SLC46A1)
PCFT is the main folate uptake transporter at the intestinal brush border and in the choroid plexus. Mutations causing it to fail result in hereditary folate malabsorption. can then actively transport across the gut wall.

rs202720 lies approximately 396 nucleotides into an intron of FOLH1 and affects at least six annotated transcripts. Because it is intronic with no coding consequence, the functional mechanism is indirect — likely a regulatory effect on FOLH1 expression levels or alternative splicing of FOLH1 isoforms. The well-studied missense variant in FOLH1, His475Tyr ⁴⁴ H475Y (rs61886492) is the most functionally characterized FOLH1 variant: it reduces intestinal GCPII enzyme activity by approximately 53% (Devlin et al. 2000, PMID 11092759)., provides a molecular model for how reduced GCPII activity translates into lower dietary folate bioavailability.

The Evidence

Direct evidence for rs202720 specifically is limited. The variant has been genotyped in an elderly Brazilian cohort⁵⁵ elderly Brazilian cohort
Mazzotti DR et al. Association of APOE, GCPII and MMP9 polymorphisms with common diseases and lipid levels. Gene, 2014 (C allele frequency 26.6%) without significant disease or lipid associations reported for this specific variant. A pathway-wide association study⁶⁶ pathway-wide association study
Boyles AL et al. Oral facial clefts and gene polymorphisms in metabolism of folate. Genet Epidemiol, 2009 of 425 case-parent triads found FOLH1 variants showed the strongest gene-level signal for cleft palate only (P=0.0008), though causality and which specific FOLH1 SNP drove the signal were not established.

The broader FOLH1/GCPII biology is well established. The functionally characterized H475Y missense variant (rs61886492) reduces GCPII enzyme activity by 53% in cellular models⁷⁷ 53% in cellular models
Devlin AM et al. Glutamate carboxypeptidase II: a polymorphism associated with lower levels of serum folate and hyperhomocysteinemia. Hum Mol Genet, 2000 and is associated with lower serum folate and higher homocysteine in population studies. A Dutch study of 791 adults found that GCPII 1561T allele carriers had significantly higher red blood cell and plasma folate⁸⁸ significantly higher red blood cell and plasma folate
Lievers KJA et al. Influence of GCPII polymorphism on plasma homocysteine, folate and vitamin B12 levels. Atherosclerosis, 2002 and lower homocysteine, suggesting the variant alters folate status beyond its direct effect on polyglutamyl cleavage — pointing to regulatory mechanisms, possibly involving expression-level differences of the type that an intronic variant like rs202720 could produce.

A controlled bioavailability study found that polyglutamyl folic acid bioavailability did not differ⁹⁹ polyglutamyl folic acid bioavailability did not differ
Melse-Boonstra A et al. Bioavailability of polyglutamyl folic acid relative to monoglutamyl folic acid. Am J Clin Nutr, 2004 significantly between GCPII genotypes (64% vs. 70%), suggesting the observed differences in folate status likely arise from changes in GCPII expression rather than altered enzyme kinetics. This mechanistic pathway — intronic variant → altered expression → changed folate absorption efficiency — is consistent with the functional category of rs202720.

Practical Actions

Given the emerging and indirect nature of the evidence, strong clinical recommendations specific to rs202720 cannot be made with confidence. However, individuals with the CC genotype who have low dietary folate intake may have reduced GCPII expression and consequently lower folate bioavailability from food sources. Supplementing with monoglutamyl forms of folate (folic acid or 5-methyltetrahydrofolate/5-MTHF) bypasses GCPII entirely: these forms do not require enzymatic deconjugation before absorption. Measuring serum folate or red blood cell folate can confirm whether absorption is adequate.

Interactions

rs202720 belongs to the broader intestinal folate absorption step, upstream of the methylation cycle. A CC genotype here compounds with any downstream methylation variant — particularly MTHFR C677T (rs1801133) and A1298C (rs1801131) — since less folate entering the cycle means less substrate for an already-impaired MTHFR enzyme. rs1051266, the SLC19A1 G80A variant controlling folate transport into cells, represents the next step in the pathway after GCPII absorption. The well-characterized FOLH1 missense variant rs61886492 (H475Y) is the primary functional variant in this gene; the relationship between rs202720 and rs61886492 in terms of linkage disequilibrium has not been formally published, making it uncertain whether they tag the same functional haplotype.