rs2242670 — KLK4

After your teeth are formed, a brief but critical window determines whether your enamel will be hard or soft for life. During this maturation phase, a serine protease called kallikrein-related peptidase 4 (KLK4)¹¹ kallikrein-related peptidase 4 (KLK4)
a digestive enzyme secreted by maturing enamel cells that degrades the protein scaffold left over from enamel construction must aggressively clear the remaining organic matrix so that enamel mineral crystals can interlock and harden into the densest tissue in the human body. Without sufficient KLK4 activity, proteins stay trapped between crystals — and the result is soft, porous enamel that cracks and decays more easily.

The rs2242670 variant lies within an intron of KLK4 on chromosome 19q13.3. Although the variant does not change the protein sequence, intronic variants can alter splice site usage, regulatory element activity, or mRNA expression levels — any of which could subtly reduce KLK4 output during the critical maturation window. Multiple independent case-control studies in European and South American populations have found the G allele associated with elevated dental caries susceptibility across both primary (baby) and permanent dentition.

KLK4 is expressed exclusively by transition- and maturation-stage ameloblasts — the specialized cells that build tooth enamel. Its job is to degrade the proteins (amelogenins, ameloblastin, enamelin)²² degrade the proteins (amelogenins, ameloblastin, enamelin)
these proteins are essential scaffolding during enamel crystal growth, but must be completely removed for crystals to expand, fuse, and harden that formed the scaffolding during the earlier secretory stage. Mice lacking KLK4 develop enamel of normal thickness and shape, but the crystals fail to interlock — they literally spill out when enamel is fractured. The teeth are rapidly ground down after eruption despite being kept on soft food.

Fluoride has a direct mechanistic connection: it suppresses TGF-β1 expression in the developing enamel organ, which in turn reduces KLK4 expression and slows protein clearance. This means the same gene that responds to fluoride deficiency also underlies common variation in caries susceptibility³³ common variation in caries susceptibility
fluoride therefore acts partly through the KLK4 pathway, supporting fluoride as a targeted intervention for people with reduced KLK4 function.

The rs2242670 G allele likely impairs KLK4 expression or mRNA processing during enamel maturation. The exact molecular mechanism has not been characterized, but the consistent clinical associations across independent populations suggest a real, if modest, effect on enamel quality.

The largest study of rs2242670 examined 761 Czech children (European Caucasian) in a case-control design spanning primary and permanent dentition. In primary (baby) teeth, the GG genotype was found in 36.2% of severe caries cases but only 20.0% of caries-free controls⁴⁴ GG genotype was found in 36.2% of severe caries cases but only 20.0% of caries-free controls
Klímová et al., Clinical Oral Investigations, 2022; n=150 primary dentition children; cases defined as dmft ≥ 10; OR 2.27, 95% CI 0.99–5.21, p=0.036. In the permanent dentition cohort (611 children, ages 13–15), the G allele was independently associated with severe caries (DMFT ≥ 6), with OR 1.39 (95% CI 0.98–1.99, p=0.040). Haplotype analysis across KLK4 variants found GAGA (combining alleles from rs2235091 and rs2242670) was a pro-carious risk factor (p=0.001 for DMFT > 0).

A replication study in 200 South Brazilian adults confirmed the association: rs2242670 maintained statistical significance in multivariate analysis alongside dental biofilm⁵⁵ rs2242670 maintained statistical significance in multivariate analysis alongside dental biofilm
Cavallari et al., Caries Research, 2017; 100 caries cases, 100 caries-free controls; multivariate model adjusted for oral hygiene, diet, and fluoride exposure. An Egyptian adult cross-sectional study (n=204) similarly found KLK4 rs2242670 alleles and genotypes correlated with dental caries susceptibility.

The evidence is consistent in direction (G allele = risk) across European and South American cohorts. Effect sizes are modest (OR approximately 1.4–2.3), as expected for common intronic variants contributing to a multifactorial condition. The biological plausibility is strong given KLK4's established essential role in enamel maturation.

Reduced KLK4 efficiency during enamel maturation is a done deal before teeth erupt — the formation window closes in early childhood and cannot be reopened. What you can do is compensate through remineralization strategy. Fluoride is particularly well-matched here, given its direct mechanistic connection to the KLK4 pathway. Consistently high fluoride exposure (topical toothpaste, varnish) supports remineralization of any softened surface enamel. Nano-hydroxyapatite and casein phosphopeptide- amorphous calcium phosphate (CPP-ACP) products provide complementary mineral delivery.

Because the variant affects enamel that was laid down in childhood, people with the GG genotype who are now adults have already lived with the consequence — and can focus on arrest and remineralization rather than prevention of formation defects. Parents who carry this variant may want to be aware when their children are in the primary dentition window (ages 6 months to 6 years).

rs2242670 has been studied alongside other KLK4 variants (rs2235091, rs2978642, rs198968) and the AMELX variant rs17878486. In the Czech cohort, haplotype analysis of KLK4 variants produced stronger signals than any individual SNP alone, consistent with multiple independent functional variants in the enamel gene cluster on chromosome 19. The AMELX-KLK4 combination represents the two sequential phases of enamel development — structural protein scaffolding (AMELX) and matrix protein clearance (KLK4) — and their co-association with caries suggests a polygenic enamel susceptibility model.