Woolly hair in tricho-dento-osseous syndrome

Tricho-dento-osseous syndrome (TDOS) is a rare ectodermal dysplasia caused by mutations in the DLX3 gene and it is not usually included as a cause of syndromic woolly hair. We present a new case of TDOS with a novel DLX3 variant and woolly hair.

Autosomal recessive congenital ichthyosis caused by a pathogenic missense variant in CLDN1

Autosomal recessive congenital ichthyosis (ARCI) refers to a large and genetically heterogenous group of non-syndromic disorders of cornification featuring diffuse scaling. Ichthyosis, leukocyte vacuoles, alopecia, and sclerosing cholangitis (ILVASC) syndrome is a rare autosomal recessive syndromic form of ichthyosis. The disease usually results from premature termination codon-causing pathogenic variants in CLDN1 encoding CLAUDIN-1 (CLDN1). We used whole exome sequencing (WES), Sanger sequencing, 3D protein modeling, Western blotting, and immunofluorescence confocal microscopy to delineate the genetic basis of ichthyosis in two siblings with ichthyosis but no other ectodermal abnormalities. One of the two siblings underwent liver transplantation in early childhood due to biliary atresia. Both patients were found to carry a homozygous missense pathogenic variant, c.242G>A (p.Arg81His), in CLDN1. The variant resulted in decreased CLDN1 expression in patient skin. 3D protein modeling predicted that p.Arg81His induces deleterious conformational changes. Accordingly, HaCaT cells transfected with a construct expressing the mutant CLDN1 cDNA featured decreased levels and mislocation of CLDN1 as compared with cells expressing the wildtype cDNA. In conclusion, we describe the first pathogenic missense variant in CLDN1 shown to result in ARCI.

Coexistence of pachyonychia congenita and hidradenitis suppurativa: more than a coincidence

BACKGROUND

The coexistence of pachyonychia congenita (PC) and hidradenitis suppurativa (HS) has been described in case reports. However, the pathomechanism underlying this association and its true prevalence are unknown.

OBJECTIVES

To determine the genetic defect underlying the coexistence of PC and HS in a large kindred, to delineate a pathophysiological signalling defect jointly leading to both phenotypes, and to estimate the prevalence of HS in PC.

METHODS

We used direct sequencing and a NOTCH luciferase reporter assay to characterize the pathophysiological basis of the familial coexistence of HS and PC. A questionnaire was distributed to patients with PC registered with the International Pachyonychia Congenita Research Registry (IPCRR) to assess the prevalence of HS among patients with PC.

RESULTS

Direct sequencing of DNA samples obtained from family members displaying both PC and HS demonstrated a missense variant (c.275A>G) in KRT17, encoding keratin 17. Abnormal NOTCH signalling has been suggested to contribute to HS pathogenesis. Accordingly, the KRT17 c.275A>G variant resulted in a significant decrease in NOTCH activity. To ascertain the clinical importance of the association of HS with PC, we distributed a questionnaire to all patients with PC registered with the IPCRR. Seventy-two of 278 responders reported HS-associated clinical features (25·9%). Disease-causing mutations in KRT17 were most prevalent among patients with a dual phenotype of PC and HS (43%).

CONCLUSIONS

The coexistence of HS and KRT17-associated PC is more common than previously thought. Impaired NOTCH signalling as a result of KRT17 mutations may predispose patients with PC to HS. What is already known about this topic? The coexistence of pachyonychia congenita (PC) and hidradenitis suppurativa (HS) has been described in case reports. However, the pathomechanism underlying this association and its true prevalence are unknown. What does this study add? A dual phenotype consisting of PC and HS was found to be associated with a pathogenic variant in KRT17. This variant was found to affect NOTCH signalling, which has been previously implicated in HS pathogenesis. HS was found to be associated with PC in a large cohort of patients with PC, especially in patients carrying KRT17 variants, suggesting that KRT17 variants causing PC may also predispose to HS. What is the translational message? These findings suggest that patients with PC have a higher prevalence of HS than previously thought, and hence physicians should have a higher level of suspicion of HS diagnosis in patients with PC.

Loss-of-function variants in KLF4 underlie autosomal dominant palmoplantar keratoderma

PURPOSE

Palmoplantar keratodermas (PPKs) form a group of disorders characterized by thickening of palm and sole skin. Over the past 2 decades, many types of inherited PPKs have been found to result from abnormal expression, processing, or function of adhesion proteins.

METHODS

We used exome and direct sequencing to detect causative pathogenic variants. Functional analysis of these variants was conducted using reverse transcription quantitative polymerase chain reaction, immunofluorescence confocal microscopy, immunoblotting, a promoter reporter assay, and chromatin immunoprecipitation.

RESULTS

We identified 2 heterozygous variants (c.1226A>G and c.633_634dupGT) in KLF4 in 3 individuals from 2 different unrelated families affected by a dominant form of PPK. Immunofluorescence staining for a number of functional markers revealed reduced epidermal DSG1 expression in patients harboring heterozygous KLF4 variants. Accordingly, human keratinocytes either transfected with constructs expressing these variants or downregulated for KLF4 displayed reduced DSG1 expression, which in turn has previously been found to be associated with PPK. A chromatin immunoprecipitation assay confirmed direct binding of KLF4 to the DSG1 promoter region. The ability of mutant KLF4 to transactivate the DSG1 promoter was significantly decreased when compared with wild-type KLF4.

CONCLUSION

Loss-of-function variants in KLF4 cause a novel form of dominant PPK and show its importance in the regulation of epidermal differentiation.

Molecular epidemiology of non-syndromic autosomal recessive congenital ichthyosis in a Middle-Eastern population

Autosomal recessive congenital ichthyosis (ARCI) is a rare and heterogeneous skin cornification disorder presenting with generalized scaling and varying degrees of erythema. Clinical manifestations range from lamellar ichthyosis (LI), congenital ichthyosiform erythroderma (CIE) through the most severe form of ARCI, Harlequin ichthyosis (HI). We used homozygosity mapping, whole-exome and direct sequencing to delineate the relative distribution of pathogenic variants as well as identify genotype-phenotype correlations in a cohort of 62 Middle Eastern families with ARCI of various ethnic backgrounds. Pathogenic variants were identified in most ARCI-associated genes including TGM1 (21%), CYP4F22 (18%), ALOX12B (14%), ABCA12 (10%), ALOXE3 (6%), NIPAL4 (5%), PNPLA1 (3%), LIPN (2%) and SDR9C7 (2%). In 19% of cases, no mutation was identified. Our cohort revealed a higher prevalence of CYP4F22 and ABCA12 pathogenic variants and a lower prevalence of TGM1 and NIPAL4 variants, as compared to data obtained in other regions of the world. Most variants (89%) in ALOX12B were associated with CIE and were the most common cause of ARCI among patients of Muslim origin (26%). Palmoplantar keratoderma associated with fissures was exclusively a result of pathogenic variants in TGM1. To our knowledge, this is the largest cohort study of ARCI in the Middle-Eastern population reported to date. Our data demonstrate the importance of population-tailored mutation screening strategies and shed light upon specific genotype-phenotype correlations.

Molecular epidemiology of pachyonychia congenita in the Israeli population

BACKGROUND

Pachyonychia congenita (PC) is a rare autosomal dominant disorder featuring palmoplantar keratoderma, nail dystrophy, oral leucokeratosis, pilosebaceous cysts and natal teeth. PC results from dominant mutations in one of five genes (KRT6A, KRT6B, KRT6C, KRT16, KRT17) encoding keratin proteins.

AIM

To delineate the clinical and genetic features of PC in a series of Israeli patients.

METHODS

We used direct sequencing of genomic DNA, and also used cDNA sequencing where applicable.

RESULTS

We collected clinical information and molecular data in a cohort of Israeli families diagnosed with PC (n = 16). Most of the patients were Ashkenazi Jews and had a family history of PC. The most common clinical findings were painful focal plantar keratoderma (94%) accompanied by nail dystrophy (81%), pilosebaceous cysts (31%) and prenatal/natal teeth (13%). In contrast to the high prevalence of KRT6A mutations in other populations, we found that KRT16 mutations were the most common type among Israeli patients with PC (56%). Most (77%) of the Israeli patients with PC with KRT16 mutation carried the same variant (c.380G>A; p.R127H) and shared the same haplotype around the KRT16 locus, suggestive of a founder effect.

CONCLUSION

The data gleaned from this study emphasizes the importance of population-specific tailored diagnostic strategies.

ST18 affects cell-cell adhesion in pemphigus vulgaris in a tumour necrosis factor-α-dependent fashion

BACKGROUND

Pemphigus vulgaris (PV) is a life-threatening mucocutaneous autoimmune blistering disease. We previously showed that genetic variants within the ST18 gene promoter area confer a sixfold increase in the propensity to develop PV. ST18, a transcription factor, was found to be overexpressed in the epidermis of patients with PV. In addition, it was found to promote autoantibody-mediated abnormal epidermal cell-cell adhesion and secretion of proinflammatory mediators by keratinocytes.

OBJECTIVES

To delineate the mechanism through which ST18 contributes to destabilization of cell-cell adhesion.

METHODS

We used quantitative reverse-transcriptase polymerase chain reaction, immunofluorescence microscopy, a luciferase reporter system, site-directed mutagenesis, chromatin immunoprecipitation (ChIP) and the dispase dissociation assay.

RESULTS

The ChIP and luciferase reporter assays showed that ST18 directly binds and activates the TNF promoter. Accordingly, increased ST18 expression contributes to PV pathogenesis by destabilizing cell-cell adhesion in a tumour necrosis factor (TNF)-α-dependent fashion. In addition, dual immunofluorescence staining showed increased expression of both ST18 and TNF-α in the skin of patients with PV carrying an ST18-associated PV risk variant, which was found to be associated with a more extensive PV phenotype.

CONCLUSIONS

Our findings suggest a role for TNF-α in mediating the deleterious effect of increased ST18 expression in PV skin.

Palmoplantar keratoderma caused by a missense variant in CTSB encoding cathepsin B

BACKGROUND

Palmoplantar keratoderma (PPK) refers to a large group of disorders characterized by extensive genetic and phenotypic heterogeneity. PPK diagnosis therefore increasingly relies upon genetic analysis.

AIM

To delineate the genetic defect underlying a case of diffuse erythematous PPK associated with peeling of the skin.

METHODS

Whole exome and direct sequencing, real-time quantitative PCR, protein modelling and a cathepsin B enzymatic assay were used.

RESULTS

The patient studied had severe diffuse erythematous PPK transgrediens. Pedigree analysis suggested an autosomal dominant mode of inheritance. Whole exome sequencing revealed a heterozygous missense mutation in the CTSB gene, encoding the cysteine protease cathepsin B. Genomic duplications in a noncoding region, which regulates the expression of CTSB, were recently found to cause erythrokeratolysis hiemalis, a rare autosomal dominant disorder of cornification. This mutation affects a highly conserved residue, and is predicted to be pathogenic. Protein modelling indicated that the mutation is likely to lead to increased endopeptidase cathepsin B activity. Accordingly, the CTSB variant was found to result in increased cathepsin B proteolytic activity.

CONCLUSION

In summary, we report the identification of the first gain-of-function missense mutation in CTSB, which was found to be associated in one individual with a dominant form of diffuse PPK.

Loss-of-function variants in C3ORF52 result in localized autosomal recessive hypotrichosis

PURPOSE

Localized autosomal recessive hypotrichosis (LAH) has been associated with pathogenic variants in DSG4, encoding a desmosomal protein as well as in LIPH and LPAR6, encoding respectively lipase H, which catalyzes the formation of 2-acyl-lysophosphatidic acid (LPA), and lysophosphatidic acid receptor 6, a receptor for LPA. LPA promotes hair growth and differentiation. In this study we aimed at delineating the genetic basis of LAH in patients without pathogenic variants in these three genes.

METHODS

Variant analysis was conducted using exome and direct sequencing. We then performed quantitative reverse transcription polymerase chain reaction (RT-qPCR), immunofluorescence staining, immunoblotting, enzymatic, and coimmunoprecipitation assays to evaluate the consequences of potential etiologic variants.

RESULTS

We identified homozygous variants in C3ORF52 in four individuals with LAH. C3ORF52 was found to be coexpressed with lipase H in the inner root sheath of the hair follicle and the two proteins were found to directly interact. The LAH-causing variants were associated with decreased C3ORF52 expression and resulted in markedly reduced lipase H-mediated LPA biosynthesis.

CONCLUSION

LAH can be caused by abnormal function of at least three proteins which are necessary for proper LPA biosynthesis.

Loss-of-Function Variants in SERPINA12 Underlie Autosomal Recessive Palmoplantar Keratoderma

Inherited palmoplantar keratodermas refer to a large and heterogeneous group of conditions resulting from abnormal epidermal differentiation and featuring thickening of the skin of the palms and soles. Here, we aimed at delineating the genetic basis of an autosomal recessive form of palmoplantar keratodermas manifesting with erythematous hyperkeratotic plaques over the palms and soles, extending to non-palmoplantar areas. Whole-exome sequencing in affected individuals revealed homozygous nonsense variants in the SERPINA12 gene. SERPINA12 encodes the visceral adipose tissue-derived serpin A12, a serine protease inhibitor. The pathogenic variants were found to result in reduced visceral adipose tissue-derived serpin A12 expression in patients' skin biopsies in comparison to healthy controls. In addition, SERPINA12 downregulation in three-dimensional skin equivalents was associated with marked epidermal acanthosis and hyperkeratosis, replicating the human phenotype. Moreover, decreased SERPINA12 expression resulted in reduced visceral adipose tissue-derived serpin A12-mediated inhibition of kallikrein 7 activity as well as decreased levels of desmoglein-1 and corneodesmosin, two known kallikrein 7 substrates, which are required for normal epidermal differentiation. The present data, taken collectively, demarcate a unique type of autosomal recessive palmoplantar keratodermas, attribute to visceral adipose tissue-derived serpin A12 a role in skin biology, and emphasize the importance of mechanisms regulating proteolytic activity for normal epidermal differentiation.

Variant PADI3 in Central Centrifugal Cicatricial Alopecia

BACKGROUND

Central centrifugal cicatricial alopecia (CCCA) is the most common form of scarring alopecia among women of African ancestry. The disease is occasionally observed to affect women in families in a manner that suggests an autosomal dominant trait and usually manifests clinically after intense hair grooming. We sought to determine whether there exists a genetic basis of CCCA and, if so, what it is.

METHODS

We used exome sequencing in a group of women with alopecia (discovery set), compared the results with those in a public repository, and applied other filtering criteria to identify candidate genes. We then performed direct sequencing to identify disease-associated DNA variations and RNA sequencing, protein modeling, immunofluorescence staining, immunoblotting, and an enzymatic assay to evaluate the consequences of potential etiologic mutations. We used a replication set that consisted of women with CCCA to confirm the data obtained with the discovery set.

RESULTS

In the discovery set, which included 16 patients, we identified one splice site and three heterozygous missense mutations in PADI3 in 5 patients (31%). (The approximate prevalence of the disease is up to 5.6%.) PADI3 encodes peptidyl arginine deiminase, type III (PADI3), an enzyme that post-translationally modifies other proteins that are essential to hair-shaft formation. All three CCCA-associated missense mutations in PADI3 affect highly conserved residues and are predicted to be pathogenic; protein modeling suggests that they result in protein misfolding. These mutations were found to result in reduced PADI3 expression, abnormal intracellular localization of the protein, and decreased enzymatic activity - findings that support their pathogenicity. Immunofluorescence staining showed decreased expression of PADI3 in biopsy samples of scalp skin obtained from patients with CCCA. We then directly sequenced PADI3 in an additional 42 patients (replication set) and observed genetic variants in 9 of them. A post hoc analysis of the combined data sets showed that the prevalence of PADI3 mutation was higher among patients with CCCA than in a control cohort of women of African ancestry (P = 0.002 by the chi-square test; P = 0.006 by Fisher's exact test; and after adjustment for relatedness of persons, P = 0.03 and P = 0.04, respectively).

CONCLUSIONS

Mutations in PADI3, which encodes a protein that is essential to proper hair-shaft formation, were associated with CCCA. (Funded by the Ram Family Foundation and others.).