rs2303067 — SPINK5 SPINK5 Lys420Glu

SPINK5 Lys420Glu — When the Skin's Protease Brake Fails

Your skin is a living wall, held together by a precisely timed demolition system. As dead cells reach the outermost layer, proteases called kallikreins¹¹ kallikreins
serine protease enzymes (KLK5, KLK7) that cleave the protein bridges holding corneocytes together, driving the orderly shedding of dead skin cells dissolve the protein links between them so they can shed naturally. The braking system for this process is a multi-domain protease inhibitor called LEKTI²² LEKTI
Lympho-Epithelial Kazal-Type Inhibitor, the protein encoded by SPINK5; contains 15 serine protease inhibitory domains and is expressed in skin, thymus, and mucous membranes, encoded by the SPINK5 gene. When LEKTI malfunctions, kallikrein proteases run unchecked — and the result is a compromised skin barrier, inflammation, and atopic disease.

The rs2303067 variant (c.1258A>G in coding notation; note that the GRCh38 plus-strand reference allele is A, which encodes Lys420, the risk form) introduces a single amino acid change in domain 6 of LEKTI: lysine at position 420 is replaced by glutamic acid (p.Lys420Glu). The G allele (Glu420) is actually the slightly more common and protective allele globally (about 52% by gnomAD v4); the A allele (Lys420) is the risk variant carried by approximately 48% of the global population. Carrying one or two copies of the A allele means your LEKTI protein is processed abnormally — with real consequences for skin barrier integrity and atopic disease risk.

The Mechanism

The Lys420 substitution (A allele) has been characterised at the molecular level by Fortugno et al. in a landmark 2012 functional study. The Lys residue at position 420 sits in the linker region between LEKTI inhibitory domains D6 and D7 — a region that is a substrate for furin, a cellular proprotein convertase³³ proprotein convertase
enzyme that cleaves precursor proteins at specific dibasic amino acid sequences, processing them into functional mature forms.

Normally, the LEKTI precursor is processed by furin into a series of overlapping inhibitory fragments. One of the most potent is the D6–D9 fragment, which has the strongest inhibitory activity against KLK5-mediated desmoglein-1 (DSG1) degradation⁴⁴ KLK5-mediated desmoglein-1 (DSG1) degradation
desmoglein-1 is a key structural protein of corneodesmosomes — the rivets holding skin cells together; when KLK5 cleaves it, desquamation proceeds; LEKTI fragment D6–D9 prevents this cleavage. The Lys420 substitution accelerates furin-mediated cleavage within the D6–D7 linker, destroying the D6–D9 fragment before it can form. The result is a functional LEKTI deficit: KLK5, KLK7, and elastase-2 are insufficiently inhibited, desmoglein-1 is over-cleaved, profilaggrin breakdown accelerates, and the skin barrier weakens. Compounding this, epidermis from Lys420/Lys420 donors shows elevated expression of TSLP⁵⁵ TSLP
thymic stromal lymphopoietin, a cytokine released by barrier- disrupted keratinocytes that drives Th2 immune skewing and atopic sensitisation, directly linking the structural barrier defect to atopic inflammation.

The Evidence

The clearest genetic signal for rs2303067 comes from disease-subtype analysis. A Slovenian case- control study by Dežman et al.⁶⁶ Dežman et al.
SPINK5 is associated with early-onset and CHI3L1 with late-onset atopic dermatitis. Int J Immunogenet, 2017 enrolled 241 atopic dermatitis patients and 164 healthy controls and found that rs2303067 was significantly associated specifically with early-onset AD (onset ≤8 years: OR=2.57, p=0.003). It was also associated with disease severity markers: hospitalization requirement (OR=2.76, p=0.006), disease duration ≥10 years (OR=2.32, p=0.008), and involvement of multiple body parts (OR=2.01, p=0.015).

The clinical significance is underscored by a 2023 case report from Moltrasio et al.⁷⁷ Moltrasio et al.
Netherton Syndrome Caused by Heterozygous Frameshift Mutation Combined with Homozygous c.1258A>G Polymorphism in SPINK5 Gene. Genes (Basel), 2023 describing a patient who developed Netherton syndrome with the combination of a heterozygous frameshift mutation AND homozygous rs2303067. The authors note that homozygous Lys420/Lys420 alone carries approximately 1.8× the population risk for atopic dermatitis, and when combined with a loss-of-function SPINK5 allele, produces haploinsufficiency sufficient for a full Netherton phenotype.

A large European population study by Weidinger et al.⁸⁸ Weidinger et al.
Analysis of SPINK5, KLK7, and FLG polymorphisms and eczema risk. J Allergy Clin Immunol, 2008 (2,774 cases, 10,607 controls) found a maternal transmission effect for rs2303067 but concluded it is not a major population-level eczema risk factor in unselected cohorts. This contrast with the Dežman study likely reflects phenotypic heterogeneity: the SPINK5 variant's effect is most pronounced in early-onset, barrier-driven atopic dermatitis — not in the broader, genetically heterogeneous eczema population. Studies of asthma alone have found no association, consistent with SPINK5's predominantly cutaneous and mucosal expression.

The Japanese population provided some of the earliest evidence. Kato et al.⁹⁹ Kato et al.
SPINK5 gene polymorphisms and atopic dermatitis in Japanese. Br J Dermatol, 2003 and Nishio et al.¹⁰¹⁰ Nishio et al.
SPINK5 polymorphisms and atopic dermatitis in Japanese. Genes Immun, 2003 both reported significant SPINK5–AD associations using transmission disequilibrium tests, establishing cross-ethnic consistency.

Practical Actions

The Lys420 allele's primary consequence is structural: impaired LEKTI activity leads to chronic subclinical protease hyperactivity in the skin, producing a leakier barrier and a lower threshold for atopic sensitisation. The actionable implications fall into three domains:

Barrier protection: Physical barrier support — particularly emollients that reduce transepidermal water loss — is specifically indicated by the mechanism, not as general skincare advice. Emollient therapy has clinical trial support for reducing AD incidence and severity, and the rationale is even stronger when LEKTI activity is constitutively reduced.

Trigger avoidance: A compromised LEKTI-mediated barrier admits allergens, irritants, and microbes more readily. This makes trigger identification — through specific IgE testing or patch testing — more productive than in barrier-intact individuals.

Monitoring for severe presentations: Homozygous Lys420 individuals (AA genotype) who also carry any second SPINK5 loss-of-function allele (rare, but present in the population) risk a Netherton-like phenotype. Severe early-onset ichthyosis, recurrent skin infections, and marked atopy in combination warrant SPINK5 gene sequencing.

Interactions

SPINK5 × FLG (filaggrin) variants: Weidinger et al. found no statistical interaction between rs2303067 and FLG loss-of-function variants (R501X, 2282del4) in their large European cohort, suggesting the two mechanisms — LEKTI impairment (protease pathway) and filaggrin loss (structural scaffold pathway) — act in parallel rather than synergistically. Carrying risk variants at both loci likely increases absolute AD risk additively. Related SPINK5 variants (rs2303065, rs2280099, rs8111930) have been examined in haplotype analyses; the Lys420Glu variant is generally the most functionally characterized within the SPINK5 locus.

SPINK5 × KLK5/KLK7 variants: Weidinger et al. also tested KLK7 (rs11567785) alongside SPINK5; neither showed interaction. The SPINK5/kallikrein axis is a candidate for compound effects, but published interaction data remain sparse.