Pathogenic variants in the filaggrin (FLG) gene cause ichthyosis vulgaris (IV) and predispose to atopic dermatitis. Hereditary palmoplantar keratoderma (PPK) can be an isolated condition or a part of another genodermatosis, such as ichthyosis. FLG variants are suggested modifiesr of PPK. To our knowledge, there are no reports describing PPK as a symptom of IV nor isolated PPK caused by variants in the FLG gene.
In this case series, 22 patients with PPK and variants in the FLG gene were included. Genetic testing was done with whole exome sequencing (18/22) and targeted analysis for FLG was performed (4/22). Phenotypical characteristics were retrieved from the patient files. Ten patients were heterozygous (FLG -/+), six homozygous and six compound heterozygous for pathogenic FLG variants (FLG -/-). Two novel variants, c.10086del and c.5842G>T, were identified. All patients presented with diffuse PPK, generalized xerosis cutis and almost all (20/22) showed hyperlinearity on the palms of the hands. This was often accompanied by palmoplantar erythema (18/22) and transgrediens (14/22). The severity was scored, with nine patients showing a mild, ten a moderate and three a severe phenotype with no significant difference between FLG -/+ and FLG -/- patients. The palmoplantar skin changes did not fit the clinical presentation of hand or feet eczema and itch was not reported.
Our cohort shows that pathogenic variants in the FLG gene can cause PPK as an IV-related symptom. The presence of eczema and/or atopy is not a prerequisite. We propose screening of the FLG gene in case of a diffuse PPK and adding PPK to the list of symptoms of IV.

LB039 - Palmoplantar keratoderma as a clinical feature of pathogenic variants in the filaggrin gene

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