Cystatin M/E Variant Causes Autosomal Dominant Keratosis Follicularis Spinulosa Decalvans by Dysregulating Cathepsins L and V.

Keratosis follicularis spinulosa decalvans (KFSD) is a rare cornification disorder with an X-linked recessive inheritance in most cases. Pathogenic variants causing X-linked KFSD have been described in MBTPS2, the gene for a membrane-bound zinc metalloprotease that is involved in the cleavage of sterol regulatory element binding proteins important for the control of transcription. Few families have been identified with an autosomal dominant inheritance of KFSD. We present two members of an Austrian family with a phenotype of KFSD, a mother and her son. The disease was not observed in her parents, pointing to a dominant inheritance with a de novo mutation in the index patient. Using whole-exome sequencing, we identified a heterozygous missense variant in CST6 in DNA samples from the index patient and her affected son. In line with family history, the variant was not present in samples from her parents. CST6 codes for cystatin M/E, a cysteine protease inhibitor. Patient keratinocytes showed increased expression of cathepsin genes CTSL and CTSV and reduced expression of transglutaminase genes TGM1 and TGM3. A relative gain of active, cleaved transglutaminases was found in patient keratinocytes compared to control cells. The variant found in CST6 is expected to affect protein targeting and results in marked disruption of the balance between cystatin M/E activity and its target proteases and eventually transglutaminases 1 and 3. This disturbance leads to an impairment of terminal epidermal differentiation and proper hair shaft formation seen in KFSD.

Two patients with Papillon-Lefèvre syndrome without periodontal involvement of the permanent dentition.

Papillon-Lefèvre syndrome (PLS) is a rare autosomal recessive genodermatosis characterized by palmoplantar keratoderma and severe periodontitis leading to premature loss of primary and permanent teeth. PLS is caused by loss-of-function mutations in CTSC, lacking functional cathepsin C, which impairs the activation of neutrophil serine proteases. Precise pathogenesis of periodontal damage is unknown. Patient 1 presented with well-demarcated, transgredient, diffuse, palmoplantar keratoderma and psoriasiform lesions from the age of 2 years. Based on severe and recurrent periodontal inflammation, his dentist had diagnosed PLS at the age of 3 years and provided a strict oral hygiene regimen with repeated adjunct antibiotic therapies. Oral acitretin 10 mg/day along with tretinoin ointment at the age of 9 greatly improved palmoplantar keratoderma. Aged 18 years, the patient exhibited an intact permanent dentition and absence of periodontal disease. Patient 2, a 30-year-old man, suffered from transgredient, diffuse, palmoplantar keratoderma with fissuring from the age of 2 months, marked psoriasiform plaques on elbows and knees, and nail dystrophy. Intriguingly, without specific dental treatment, teeth and dental records were unremarkable. He was referred with a suspected diagnosis of psoriasis. Both patients were otherwise healthy, blood tests and sonography of internal organs were within normal limits. Panel sequencing revealed loss-of-function mutations in CTSC, c.322A>T (p.Lys108Ter) and c.504C>G (p.Tyr168Ter) in patient 1 and homozygous c.415G>T (p.Gly139Ter) in patient 2. The final diagnosis of unusual PLS was made. PLS should be considered in palmoplantar keratoderma lacking periodontitis or tooth loss.

Enhanced Expression of Genes Related to Xenobiotic Metabolism in the Skin of Patients with Atopic Dermatitis but Not with Ichthyosis Vulgaris.

Previous transcriptome analyses underscored the importance of immunological and skin barrier abnormalities in atopic dermatitis (AD). We sought to identify pathogenic pathways involved in AD by comparing the transcriptomes of AD patients stratified for filaggrin (FLG)-null mutations to those of both healthy donors and patients with ichthyosis vulgaris. We applied RNA sequencing to analyze the whole transcriptome of nonlesional skin. We found that 607 genes (476 up-regulated and 131 down-regulated by >2-fold) and 193 genes (172 up-regulated and 21 down-regulated by >2-fold) were differentially expressed when all AD or ichthyosis vulgaris patients were compared with healthy donors, respectively. Expression of genes involved in RNA/protein turnover and adenosine triphosphate synthesis, as well as genes involved in cell death, response to oxidative stress, DNA damage/repair, and autophagy, were significantly enriched in AD skin and, to a lesser extent, in ichthyosis vulgaris skin. FLG-null mutations appear to hardly interfere with current observations. Genes related to xenobiotic metabolism were up-regulated in AD skin only, as were genes related to arachidonic, linoleic, and α-linolenic acid metabolism. Thus, this work newly links AD pathogenesis to aberrant expression of genes related to xenobiotic metabolism.

Alterations in Epidermal Eicosanoid Metabolism Contribute to Inflammation and Impaired Late Differentiation in FLG-Mutated Atopic Dermatitis.

Loss-of-function mutations in the FLG gene cause ichthyosis vulgaris (IV) and represent the major predisposing genetic risk factor for atopic dermatitis (AD). Although both conditions are characterized by epidermal barrier impairment, AD also exhibits signs of inflammation. This work was aimed at delineating the role of FLG loss-of-function mutations on eicosanoid metabolism in IV and AD. Using human epidermal equivalents (HEEs) generated with keratinocytes isolated from nonlesional skin of patients with FLG wild-type AD (WT/WT), FLG-mutated AD (FLG/WT), IV (FLG/FLG), or FLG WT control skin, we assessed the potential autocrine role of epidermal-derived eicosanoids in FLG-associated versus FLG-WT AD pathogenesis. Ultrastructural analyses demonstrated abnormal stratum corneum lipid architecture in AD and IV HEEs, independent of FLG genotype. Both AD (FLG/WT) and IV (FLG/FLG) HEEs showed impaired late epidermal differentiation. Only AD (FLG/WT) HEEs exhibited significantly increased levels of inflammatory cytokines. Analyses of lipid mediators revealed increased arachidonic acid and 12-lipoxygenase metabolites. Whereas treatment of control HEEs with arachidonic acid increased expression of inflammatory cytokines, 12-hydroxy-eicosatetraenoic acid attenuated expression of late differentiation markers. Thus, FLG mutations lead to alterations in epidermal eicosanoid metabolism that could serve as an autocrine trigger of inflammation and impaired late epidermal differentiation in AD.