BG11 Palmoplantar keratoderma with mutations in filaggrin and desmoglein-1 genes

Abstract

Abstract Hereditary palmoplantar keratoderma (PPK) has many forms, and genetic testing can help distinguish diagnoses. This case demonstrates a presentation of PPK with an altered phenotype caused by a mutation in FLG. The patient was a 23-year-old woman referred with PPK since the age of 6 years. She reported dry skin on the back of her hands from infancy and no other dermatological conditions. She denied plantar pain except when there were fissures in the callus. There was no relevant past medical history, but a significant family history of individuals with PPK and curly hair, and sudden infant death (SID) in two siblings. Physical examination revealed focal plantar keratoderma bilaterally, curly hair, mild tongue leukokeratosis and generally dry skin on both legs. She had palmar hyperlinearity, small calluses on the palms and normal nails. She declined a skin biopsy. The patient was referred to cardiology to rule out cardiomyopathy associated with a desmoplakin variant. She had an unremarkable transthoracic echocardiography and cardiac magnetic resonance imaging. Twelve-lead electrocardiography showed sinus rhythm with biphasic T-wave in V2 and inverted V1. Clinically arrhythmogenic right ventricular cardiomyopathy (ARVC) was ruled out; however, given her significant family history of SID and PPK, panel testing for genes associated with ARVC was performed, which revealed a heterozygous variant of uncertain significance in MYBPC3 (p.Val639lle). This variant did not explain the patient’s PPK; therefore, a PPK panel was performed. Next-generation sequencing identified a heterozygous DSG1 [c430A>T p.(Arg.144*)] pathogenic variant and a heterozygous FLG [c2282_2285del p.(Ser761Cysfs*36)] pathogenic variant. The patient’s PPK was more severe on the plantar surface of the feet than one might expect with a DSG1 variant. This case demonstrates the interaction between two genetic variants known to be associated with skin conditions. Ichthyosis vulgaris is caused by FLG variants. Patients with heterozygous FLG variants are less severely affected and have reduced penetrance compared to homozygotes. Meanwhile, heterozygous pathogenic variants in DSG1 are associated with keratosis palmoplantaris striata I (MIM148700). We hypothesize that the coexistence of FLG and DSG1 variants may contribute to a more extensive keratoderma phenotype than usually seen with DSG1 variants. This case contributes to our understanding of PPK, demonstrates the value of genetic testing in dermatological conditions and describes a unique phenotype in the presence of multiple genetic variants. Further research is required to better understand the interaction between variants in PPK pathogenesis.