rs372628716 — FLG S3247X

FLG S3247X — A European Filaggrin Null Allele

Filaggrin is the structural protein that holds the outermost layer of skin together, retains moisture, and keeps allergens out. The FLG gene encodes profilaggrin¹¹ profilaggrin
a large precursor protein cleaved into 10–12 filaggrin monomers during terminal epidermal differentiation, which aggregate keratin filaments into the waterproof matrix of the stratum corneum. S3247X (c.9740C>A on the coding strand) introduces a premature stop codon at position 3247 of the protein, truncating the C-terminal region and eliminating filaggrin production from that allele — making it a filaggrin null mutation with the same functional consequence as the more common R501X and 2282del4 variants.

S3247X is one of four European FLG null mutations (alongside R501X, 2282del4, and R2447X) that together account for more than 90% of FLG mutations found in European populations. Its allele frequency in European-ancestry populations (~0.25–0.28%) is substantially lower than R501X (~1.6%) or 2282del4 (~2.1%), making it a minor but clinically significant member of this group. The variant is essentially absent in East Asian, African, and South Asian populations, reflecting the distinct FLG mutation spectra across ancestry groups.

The Mechanism

S3247X truncates the C-terminal region of profilaggrin, which contains the final filaggrin repeat unit and the C-terminal domain required for correct profilaggrin processing. Loss of the C-terminal domain prevents orderly cleavage of profilaggrin into filaggrin monomers²² Loss of the C-terminal domain prevents orderly cleavage of profilaggrin into filaggrin monomers
The C-terminus of profilaggrin is essential for targeting to keratohyalin granules and for the proteolytic cascade that releases individual filaggrin units during terminal epidermal differentiation. The resulting filaggrin deficiency from the affected allele reduces total filaggrin protein by approximately 50% in heterozygotes, directly impairing natural moisturizing factor (NMF)³³ natural moisturizing factor (NMF)
a hygroscopic mixture of amino acids, urocanic acid, pyrrolidone carboxylic acid, urea, and ions that keeps the stratum corneum hydrated and maintains the acidic skin pH that suppresses pathogens and controls inflammation production and stratum corneum structural integrity.

Without adequate NMF and filaggrin-mediated keratin organization, transepidermal water loss (TEWL) increases⁴⁴ transepidermal water loss (TEWL) increases
TEWL measures water evaporating through skin; elevated TEWL signals barrier failure and correlates with eczema severity, skin pH rises above the optimal acidic range, serine protease activity becomes dysregulated, and gaps between corneocytes allow environmental allergens — house dust mite, pollen, food proteins — to penetrate into the viable epidermis and trigger IgE sensitization. This is the molecular basis of the atopic march.

The Evidence

S3247X was characterized as one of the four major European FLG null mutations in a population genetics study⁵⁵ population genetics study
Sandilands et al. 2009: comprehensive survey of FLG null allele frequencies in ichthyosis vulgaris and atopic eczema populations across Europe, establishing geographic gradients and population-specific frequencies. Its allele frequency shows a north-south gradient in Europe, being more prevalent in Northern and Central European populations and lower in Mediterranean and Eastern European populations.

A study of 462 Austrian and German AD patients⁶⁶ study of 462 Austrian and German AD patients
Greisenegger et al. 2010: case-control study demonstrating all four FLG null mutations (R501X, 2282del4, R2447X, S3247X) are significantly associated with AD; mutation carriers had earlier onset and higher serum IgE levels confirmed a strong association of all four mutations with atopic dermatitis. Mutation carriers showed significantly higher proportions of early-onset disease and elevated serum IgE, and overrepresentation of null alleles was seen in AD patients with concurrent asthma. Subjects with the S3247X mutation specifically were noted to be more likely to report that their skin was symptom-free at any given time compared to carriers of R501X or 2282del4, suggesting reduced penetrance relative to the most common alleles.

The semidominant inheritance pattern for FLG null mutations is well-established across the group: heterozygotes have elevated eczema risk (OR approximately 3.1; meta-analysis from 24 studies, 95% CI 2.57–3.79) and variable ichthyosis vulgaris penetrance, while compound heterozygotes and homozygotes⁷⁷ compound heterozygotes and homozygotes
individuals carrying two different FLG null mutations on separate chromosomes — functionally equivalent to having no working FLG alleles have substantially more severe disease. Compound heterozygosity with R501X/S3247X has been documented in severe AD cases.

Practical Actions

S3247X carriers have a skin barrier functioning at reduced capacity. The central intervention is external barrier support: ceramide-dominant emollients⁸⁸ ceramide-dominant emollients
formulations containing ceramides, cholesterol, and free fatty acids in a roughly 3:1:1 molar ratio most closely replicate the physiologic lipid composition of the stratum corneum compensate for reduced NMF production. Fragrance, sodium lauryl sulfate, methylisothiazolinone, and propylene glycol in personal care products all exacerbate barrier disruption disproportionately in filaggrin-insufficient skin and should be eliminated.

S3247X carriers who develop eczema should be aware of elevated risk of eczema herpeticum⁹⁹ eczema herpeticum
disseminated herpes simplex virus infection of eczematous skin, presenting as rapidly spreading punched-out vesicles or erosions — a medical emergency requiring urgent antiviral treatment, which is elevated across all FLG null carriers.

For infants in families carrying S3247X, daily emollient application from birth¹⁰¹⁰ daily emollient application from birth
supported by RCT evidence; Simpson et al. 2014 showed 50% reduction in cumulative atopic dermatitis incidence over 6 months in high-risk infants and early oral introduction of common allergens (peanut, egg, fish) per current guidelines are the two highest-impact preventive strategies for interrupting the atopic march before it starts.

Interactions

S3247X interacts with all other FLG null mutations as a compound heterozygote. When one chromosome carries S3247X and the other carries R501X (rs61816761), 2282del4 (rs558269137), or R2447X, the individual has no functional FLG allele — equivalent to homozygosity — with the most severe disease phenotype: overt ichthyosis vulgaris, high-penetrance early-onset eczema, elevated IgE sensitization, and increased asthma risk through the eczema-asthma compound pathway. Compound heterozygosity with R501X/S3247X has been documented in US severe AD cohorts.

Proposed compound action for supervisor: When a user carries rs372628716 GT or TT AND rs61816761 AG or AA, OR rs558269137 DI or DD (one null allele from S3247X and one from either R501X or 2282del4), they are compound heterozygous and effectively FLG-null. The combined recommendation should parallel that for R501X homozygosity: twice-daily ceramide-dominant emollient therapy, dermatology referral for ichthyosis and eczema management, dupilumab discussion if eczema is moderate-to-severe, early allergen introduction in offspring, elimination of all barrier-disrupting personal care ingredients, and awareness of eczema herpeticum warning signs. Evidence level: established (same disease mechanism as documented FLG-null compound heterozygotes).