rs2235373 — IRF6

IRF6 and the Genetics of Facial Formation — When a Transcription Factor Falls Short

During the sixth to ninth week of human embryonic development, precisely timed signals from a handful of transcription factors orchestrate the fusion of the facial prominences that will become the lip and palate. IRF6 — interferon regulatory factor 6¹¹ interferon regulatory factor 6
a transcription factor that controls keratinocyte proliferation and differentiation in the developing oral and facial epithelium — sits near the top of this hierarchy. When IRF6 function is severely disrupted, the result is Van der Woude syndrome (cleft lip/palate with lip pits) or popliteal pterygium syndrome, inherited in an autosomal dominant pattern. But subtler common variants in IRF6 also influence risk, pushing individuals toward or away from non-syndromic cleft lip with or without cleft palate²² non-syndromic cleft lip with or without cleft palate
NSCL/P — the most common craniofacial birth defect, affecting approximately 1 in 700 births worldwide, with no associated syndrome.

rs2235373 lies deep within an intron of IRF6 on chromosome 1q32.2, 37 nucleotides past the nearest exon boundary. It does not alter the protein sequence but sits within a region harboring regulatory elements that fine-tune IRF6 expression and splicing during the critical developmental window. The variant has been identified as the sentinel SNP for the IRF6 signal at 1q32.2³³ sentinel SNP for the IRF6 signal at 1q32.2
the lead variant capturing the IRF6 association in secondary GWAS analysis of cleft phenotypes and appears in strong linkage disequilibrium with rs642961 (a coding missense variant, V274I) and rs2235371, two other IRF6 variants studied across dozens of NSCL/P case-control populations.

The Mechanism

IRF6 protein contains a highly conserved DNA-binding domain and a protein interaction domain. During facial development it acts as a master regulator of the oral epithelial cells that must fuse, differentiate, and eventually undergo controlled programmed death to allow complete palate closure. Loss-of-function IRF6 mutations disrupt this cellular choreography — periderm cells fail to differentiate properly and form adhesions that prevent fusion, leaving a gap in the lip or palate.

The rs2235373 A allele's contribution is subtler. As an intronic variant, its effect is likely mediated through altered transcription factor binding at nearby regulatory elements, changes in splicing efficiency, or effects on chromatin accessibility during the developmental window when IRF6 dosage is most critical. No single molecular mechanism has been characterized for this specific SNP, but its location in strong LD with the better-studied IRF6 regulatory variants suggests it tags — rather than directly causes — a functional change in IRF6 expression or activity.

IRF6 is expressed predominantly in skin and squamous epithelial tissues (highest expression in esophagus, ~31 RPKM; skin, ~34 RPKM; broadly in gastrointestinal mucosa). This expression pattern reflects its primary role in epithelial biology rather than immune signaling, despite belonging to the interferon regulatory factor family.

The Evidence

The IRF6 locus at 1q32.2 has been one of the most consistently replicated non-HLA associations with NSCL/P in genetic studies spanning over two decades. rs2235373 specifically has been examined across multiple population-stratified studies.

A landmark 2007 study by Park and colleagues examined 297 case-parent trios from four populations⁴⁴ Park and colleagues examined 297 case-parent trios from four populations
European American, Taiwanese, Singaporean, and Korean; 13 SNPs across IRF6 were genotyped. Evidence of linkage and association was observed across all four groups, with haplotype analysis in Taiwanese cases producing particularly strong signals: the AGC/CGC diplotype increased cleft risk approximately 7-fold in that sample.

Population heterogeneity is a consistent theme. A 2026 meta-analysis by Muruganantham and Veerabathiran pooled 17 studies totaling 1,809 cases and 3,164 controls⁵⁵ Muruganantham and Veerabathiran pooled 17 studies totaling 1,809 cases and 3,164 controls
from Chinese Han, Brazilian, South Indian, Northeast Chinese, Uyghur, Indonesian, Vietnamese, Mesoamerican, and Iranian populations and found that rs2235373 showed significant association specifically in the dominant model, while rs2235371 showed significance in the allelic model — underscoring that different IRF6 variants capture different signals across populations.

In contrast, a larger 2026 MOOSE-compliant meta-analysis of 53 case-control studies by Sahu and colleagues⁶⁶ meta-analysis of 53 case-control studies by Sahu and colleagues
examining six IRF6 polymorphisms found that rs2235373 did not reach significance in the overall analysis, while rs642961 (OR 1.31, 95% CI 1.10–1.55) and rs2235371 (OR 0.74, 95% CI 0.60–0.92) did — suggesting that rs2235373 may act primarily as a tag SNP in high-LD with the functional variants, with population-specific LD structure determining when the tagging relationship holds.

The highest A allele frequency is in East Asian populations (~47%), where the association signal tends to be strongest. In European populations, A allele frequency is approximately 18%, and effect sizes are generally smaller.

Practical Significance

NSCL/P is the clinical context of this variant. It is a birth defect affecting the lip, palate, or both, typically requiring surgical correction in infancy and often additional dental, speech, and orthodontic treatment across childhood and adolescence. rs2235373 is a low-penetrance susceptibility allele — the vast majority of A allele carriers are unaffected. Risk is shaped by multiple genetic loci (8q24, 17q22, 10q25, and others in addition to IRF6), environmental exposures during pregnancy, and gene-environment interactions.

For adults who carry the A allele and have not themselves been affected, the primary relevance is reproductive: this variant contributes to the polygenic risk their children inherit. Periconceptional folate supplementation has demonstrated consistent reduction in NSCL/P risk in epidemiological studies, acting independently of folate's role in neural tube defect prevention. Tobacco exposure and maternal alcohol use in the first trimester further elevate risk for individuals with IRF6 susceptibility alleles.

Interactions

The IRF6 locus harbors several variants in varying degrees of linkage disequilibrium: rs642961 (V274I missense, the most-studied coding change), rs2235371 (protective), rs2235375, and rs2013162. These may represent partially independent signals or may tag the same underlying functional change depending on population. The 8q24 locus (rs987525) is a separate, independently associated risk factor for NSCL/P with an even larger effect (OR ~1.71) and combines additively with IRF6 variants in determining overall cleft risk. Individuals carrying risk alleles at both loci have substantially higher lifetime offspring risk than those carrying risk at either alone.