BACKGROUND: Epidermal differentiation disorders (EDDs, a.k.a. ichthyosis and palmoplantar keratoderma) are severe heritable skin conditions characterized by localized or generalized skin scaling and erythema. OBJECTIVES: To identify novel genetic variants causing palmoplantar keratoderma (PPK) and progressive symmetric erythrokeratoderma (PSEK) phenotypes. METHODS: We performed whole exome sequencing in a large EDD cohort including PPK and PSEK phenotypes to identify novel genetic variants. We investigated the variant consequence using in silico predictions, assays in patient keratinocytes, high-resolution spatial transcriptomics, and quantitative cytokine profiling. RESULTS: We identified three unrelated kindreds with autosomal dominant transmission of heterozygous SLURP1 variants affecting the same amino acid within the signal peptide (c.65C>
A, p.A22D, and c.65C>
T, p.A22V). One (p.A22V) had isolated PPK, and two others (p.A22D) had PSEK and PPK. In silico modeling suggested that both variants alter pro-SLURP1 cleavage, appending two amino acids to the secreted protein, which we subsequently confirmed with mass spectrometry. In patient keratinocytes we found increased differentiation-induced SLURP1 expression and secretion compared to healthy control cells. Spatial transcriptomics revealed increased NF-κB signaling and innate immune activity which may contribute to epidermal hyperproliferation in dominant SLURP1-PPK/PSEK. CONCLUSIONS: Our results expand the phenotypic spectrum of EDD due to SLURP1 pathogenic variants. While autosomal recessive Mal de Meleda is due to biallelic loss-of-function SLURP1 variants, our finding of autosomal dominant SLURP1 pathogenic variants in kindreds with PPK and PSEK suggests a novel mechanism of action. We found that heterozygous p.A22V and p.A22D SLURP1 variants append two amino acids to secreted SLURP1, increase differentiation-induced SLURP1 expression and secretion, and upregulate NF-κB signaling in PSEK cases.