Ofer Sarig

Desmoglein 1 deficiency results in severe dermatitis, multiple allergies and metabolic wasting

The relative contribution of immunological dysregulation and impaired epithelial barrier function to allergic diseases is still a matter of debate. Here we describe a new syndrome featuring severe dermatitis, multiple allergies and metabolic wasting (SAM syndrome) caused by homozygous mutations in DSG1. DSG1 encodes desmoglein 1, a major constituent of desmosomes, which connect the cell surface to the keratin cytoskeleton and have a crucial role in maintaining epidermal integrity and barrier function. Mutations causing SAM syndrome resulted in lack of membrane expression of DSG1, leading to loss of cell-cell adhesion. In addition, DSG1 deficiency was associated with increased expression of a number of genes encoding allergy-related cytokines. Our deciphering of the pathogenesis of SAM syndrome substantiates the notion that allergy may result from a primary structural epidermal defect.

Familial Pityriasis Rubra Pilaris Is Caused by Mutations in CARD14

Pityriasis rubra pilaris (PRP) is a papulosquamous disorder phenotypically related to psoriasis. The disease has been occasionally shown to be inherited in an autosomal-dominant fashion. To identify the genetic cause of familial PRP, we ascertained four unrelated families affected by autosomal-dominant PRP. We initially mapped PRP to 17q25.3, a region overlapping with psoriasis susceptibility locus 2 (PSORS2 [MIM 602723]). Using a combination of linkage analysis followed by targeted whole-exome sequencing and candidate-gene screening, we identified three different heterozygous mutations in CARD14, which encodes caspase recruitment domain family, member 14. CARD14 was found to be specifically expressed in the skin. CARD14 is a known activator of nuclear factor kappa B signaling, which has been implicated in inflammatory disorders. Accordingly, CARD14 levels were increased, and p65 was found to be activated in the skin of PRP-affected individuals. The present data demonstrate that autosomal-dominant PRP is allelic to familial psoriasis, which was recently shown to also be caused by mutations in CARD14.

Desmoglein-1/Erbin interaction suppresses ERK activation to support epidermal differentiation

Genetic disorders of the Ras/MAPK pathway, termed RASopathies, produce numerous abnormalities, including cutaneous keratodermas. The desmosomal cadherin, desmoglein-1 (DSG1), promotes keratinocyte differentiation by attenuating MAPK/ERK signaling and is linked to striate palmoplantar keratoderma (SPPK). This raises the possibility that cutaneous defects associated with SPPK and RASopathies share certain molecular faults. To identify intermediates responsible for executing the inhibition of ERK by DSG1, we conducted a yeast 2-hybrid screen. The screen revealed that Erbin (also known as ERBB2IP), a known ERK regulator, binds DSG1. Erbin silencing disrupted keratinocyte differentiation in culture, mimicking aspects of DSG1 deficiency. Furthermore, ERK inhibition and the induction of differentiation markers by DSG1 required both Erbin and DSG1 domains that participate in binding Erbin. Erbin blocks ERK signaling by interacting with and disrupting Ras-Raf scaffolds mediated by SHOC2, a protein genetically linked to the RASopathy, Noonan-like syndrome with loose anagen hair (NS/LAH). DSG1 overexpression enhanced this inhibitory function, increasing Erbin-SHOC2 interactions and decreasing Ras-SHOC2 interactions. Conversely, analysis of epidermis from DSG1-deficient patients with SPPK demonstrated increased Ras-SHOC2 colocalization and decreased Erbin-SHOC2 colocalization, offering a possible explanation for the observed epidermal defects. These findings suggest a mechanism by which DSG1 and Erbin cooperate to repress MAPK signaling and promote keratinocyte differentiation.

RIN2 Deficiency Results in Macrocephaly, Alopecia, Cutis Laxa, and Scoliosis: MACS Syndrome

Inherited disorders of elastic tissue represent a complex and heterogeneous group of diseases, characterized often by sagging skin and occasionally by life-threatening visceral complications. In the present study, we report on an autosomal-recessive disorder that we have termed MACS syndrome (macrocephaly, alopecia, cutis laxa, and scoliosis). The disorder was mapped to chromosome 20p11.21-p11.23, and a homozygous frameshift mutation in RIN2 was found to segregate with the disease phenotype in a large consanguineous kindred. The mutation identified results in decreased expression of RIN2, a ubiquitously expressed protein that interacts with Rab5 and is involved in the regulation of endocytic trafficking. RIN2 deficiency was found to be associated with paucity of dermal microfibrils and deficiency of fibulin-5, which may underlie the abnormal skin phenotype displayed by the patients.

Population-Specific Association between a Polymorphic Variant in ST18, Encoding a Pro-Apoptotic Molecule, and Pemphigus Vulgaris

Pemphigus vulgaris (PV) is a severe autoimmune blistering disease caused by anti-epithelial antibodies, leading to disruption of cell-cell adhesion. Although the disease is exceedingly rare worldwide, it is known to be relatively prevalent in Jewish populations. The low prevalence of the disease represents a significant obstacle to a genome-wide approach to the mapping of susceptibility genes. We reasoned that the study of a genetically homogeneous cohort characterized by a high prevalence of PV may help exposing associated signals while reducing spurious results due to population sub-structure. We performed a genome-wide association study using 300K single-nucleotide polymorphisms (SNPs) in a case-control study of 100 PV patients of Jewish descent and 397 matched control individuals, followed by replication of significantly associated SNPs in three additional cohorts of Jewish, Egyptian, and German origin. In addition to the major histocompatibility complex locus, a genomic segment on 8q11.23 that spans the ST18 gene was also found to be significantly associated with PV. This association was confirmed in the Jewish and Egyptian replication sets but not in the German sample, suggesting that ST18-associated variants may predispose to PV in a population-specific manner. ST18 regulates apoptosis and inflammation, two processes of direct relevance to the pathogenesis of PV. Further supporting the relevance of ST18 to PV, we found this gene to be overexpressed in the skin of PV patients as compared with healthy individuals.

Inflammatory Peeling Skin Syndrome Caused by a Mutation in CDSN Encoding Corneodesmosin

TO THE EDITOR Peeling skin syndrome (PSS) refers to a heterogeneous group of disorders characterized by superficial detachment of the epidermal corneal layers (HachamZadeh and Holubar, 1985). Two major forms of PSS have been recognized: acral PSS (MIM609796), caused by mutations in TGM5, encoding transglutaminase 5 (Cassidy et al., 2005; Kharfi et al., 2009), and generalized PSS (MIM270300), which has been subclassified into a noninflammatory type (type A PSS), the etiology of which remains unknown, and an inflammatory type (type B), which was recently shown to be associated in a large family with a recessive mutation in CDSN, encoding corneodesmosin (Oji et al., 2010). In the present study, we report the second mutation in CDSN underlying type B PSS. A 32-year-old man was referred for investigation because of a congenital pruritic and generalized rash. The patient was of Jewish origin, and his parents were first-degree cousins. A younger sister displayed similar dermatological findings (Figure 1a). The patient said that 3 days after his birth, widespread reddish, peeling skin areas had appeared over his legs, arms, and trunk, along with redness and edema of the face. The rash has been present ever since, with rare periods of mild improvement, mainly in the spring (Figure 1b and c). From the age of 10, his nails have been thick and yellowish. Complete blood cell count and blood chemistry were within normal ranges, but IgE levels were markedly elevated (30,375 IU ml ; N1⁄4 0–100). Fungal cultures from nail scrapings were negative. Hair microscopy revealed normal hair shaft structures. A skin biopsy showed mild hyperkeratosis, parakeratosis, intracorneal and subcorneal separation, hypergranulosis, and acanthosis. In the dermis, a perivascular mononuclear infiltrate and scattered eosinophils were seen (Figure 1d). The patient provided written and informed consent according to a protocol approved by the local Helsinki Committee and by the Committee for Genetic Studies of the Israeli Ministry of Health. DNA was extracted from peripheral blood leukocytes using the salt/ chloroform extraction method. Biological materials were unavailable from the patient’s family members. Genomic DNA was PCR-amplified using primer pairs spanning the entire coding sequence as well as intron–exon boundaries of the CDSN gene as described elsewhere (Oji et al., 2010). A homozygous single-nucleotide deletion was identified in exon 2 at nucleotide position 743 (accession number NC_000000.11) (Figure 1e). The mutation, termed c.746delG, is predicted to lead to frame shift and to generate a premature stop codon 40 bp downstream of the deletion (p.G249VfsX40). The mutation can be predicted to result either in the synthesis of a truncated corneodesmosin protein or in messenger RNA transcript decay. We confirmed the presence of the mutation in the patient’s DNA sequence using a PCR–restriction fragment length polymorphism assay, whereby a 183-bp-long DNA fragment was amplified using mutation-specific forward primer 50-CCCCTACATCCCC AGCTCCCACTCTGTGAC-30 and reverse primer 50-ACCTCGTAGCCACCATAG GA-30 (Figure 1f). Mutation c.746delG abolishes a recognition site for DNA endonucleases AhdI. We also used this allele-specific PCR–restriction fragment length polymorphism assay to exclude the presence of the mutation in a panel of 50 population-matched control subjects. Superficial intraepidermal detachment has been described in a number of inherited disorders, including ichthyosis bullosa of Siemens (Rothnagel et al., 1994), epidermolysis bullosa simplex superficialis (Fine et al., 1989), Netherton syndrome (Geyer et al., 2005), and PSS. Recently, a mutation in CDSN, encoding corneodesmosin, was found to segregate with PSS type B (Oji et al., 2010) in a large Roma family. In the present study, we report the second pathogenic mutation in CDSN, thus confirming the causative role of these mutations in the pathogenesis of inflammatory PSS. CDSN codes for corneodesmosin, a secreted glycoprotein that is a component of the modified desmosomal plaques in the uppermost layers of the epidermis. Corneodesmosin molecules have been shown to interact through their glycine loop domains in a homophilic fashion to mediate adhesive interactions between corneocytes (Jonca et al., 2002). Corneodesmosin has also been shown to be expressed in the inner root sheath of hair follicles (Gallinaro et al., 2004). CDSN mutations have previously been associated with autosomal dominant hypotrichosis simplex (MIM146520) (Levy-Nissenbaum et al., 2003). In this disease the mutant corneodesmosin was found to exert a toxic effect on hair follicles via the formation of amyloidosis deposits (Caubet et al., 2010). Polymorphisms in the CDSN gene have also been found in association with psoriasis (Tazi Ahnini et al., 1999). More recently, ablation of CDSN in mice was found to result in lethal epidermal permeability disruption (Matsumoto et al., 2008; Leclerc et al., 2009), in line with similar data obtained with ablation of another component of the epidermal barrier, filaggrin (Fallon et al., 2009). See related commentary on pg 561

CEDNIK syndrome results from loss-of-function mutations in SNAP29.

Background  CEDNIK (cerebral dysgenesis, neuropathy, ichthyosis and keratoderma) syndrome is a rare genodermatosis which was shown 5 years ago in one family to be associated with a loss‐of‐function mutation in SNAP29, encoding a member of the SNARE family of proteins. Decrease in SNAP29 expression was found to result in abnormal lamellar granule maturation leading to aberrant epidermal differentiation and ichthyosis.

Functional Characterization of SAMD9, a Protein Deficient in Normophosphatemic Familial Tumoral Calcinosis

Dystrophic cutaneous calcinosis is associated with disorders as common as autoimmune diseases and cancer. To get insight into the pathogenesis of this poorly understood process, we studied the function of SAMD9, a protein of unknown function, recently shown to be deficient in a hereditary form of dystrophic calcification in the skin, known as normophosphatemic familial tumoral calcinosis (NFTC). Consistent with the fact that in NFTC severe inflammatory manifestations always precede cutaneous calcinosis, we found out that SAMD9 is tightly regulated by interferon-γ (IFN-γ). In addition, the SAMD9 promoter was also found to respond strongly to IFN-γ in a luciferase reporter assay. Of interest, we identified a critical 30-bp fragment upstream to the SAMD9 transcription initiation site responsible for driving most of the gene expression. Bioinformatic analysis suggested that SAMD9 function involves interaction with additional protein(s). Using the Ras recruitment system assay and confirmatory immunoprecipitation, we demonstrated that SAMD9 interacts with RGL2. To study the biological importance of this interaction, we assessed the effect of RNA interference-mediated downregulation of this pair of proteins in various cell lines. We found out that downregulation of any of the two protein partners caused increased expression of EGR1, a transcription factor with a known role in the regulation of tissue calcification, inflammation, and cell migration. Supporting the physiological relevance of these data, EGR1 levels were also upregulated in a fibroblast cell line derived from an NFTC patient. In conclusion, our data indicate that SAMD9, an IFN-γ-responsive protein, interacts with RGL2 to diminish the expression of EGR1, a protein of direct relevance to the pathogenesis of ectopic calcification and inflammation.

Short Stature, Onychodysplasia, Facial Dysmorphism, and Hypotrichosis Syndrome Is Caused by a POC1A Mutation

Disproportionate short stature refers to a heterogeneous group of hereditary disorders that are classified according to their mode of inheritance, clinical skeletal and nonskeletal manifestations, and radiological characteristics. In the present study, we report on an autosomal-recessive osteocutaneous disorder that we termed SOFT (short stature, onychodysplasia, facial dysmorphism, and hypotrichosis) syndrome. We employed homozygosity mapping to locate the disease-causing mutation to region 3p21.1-3p21.31. Using whole-exome-sequencing analysis complemented with Sanger direct sequencing of poorly covered regions, we identified a homozygous point mutation (c.512T>C [p.Leu171Pro]) in POC1A (centriolar protein homolog A). This mutation was found to cosegregate with the disease phenotype in two families. The p.Leu171Pro substitution affects a highly conserved amino acid residue and is predicted to interfere with protein function. Poc1, a POC1A ortholog, was previously found to have a role in centrosome stability in unicellular organisms. Accordingly, although centrosome structure was preserved, the number of centrosomes and their distribution were abnormal in affected cells. In addition, the Golgi apparatus presented a dispersed morphology, cholera-toxin trafficking from the plasma membrane to the Golgi was aberrant, and large vesicles accumulated in the cytosol. Collectively, our data underscore the importance of POC1A for proper bone, hair, and nail formation and highlight the importance of normal centrosomes in Golgi assembly and trafficking from the plasma membrane to the Golgi apparatus.

A Mutation in LIPN, Encoding Epidermal Lipase N, Causes a Late-Onset Form of Autosomal-Recessive Congenital Ichthyosis

Autosomal-recessive congenital ichthyoses represent a large and heterogeneous group of disorders of epidermal cornification. Recent data suggest that most of these disorders might result from defective lipid transport and metabolism. In the present study, we describe a late-onset form of recessive ichthyosis in a large consanguineous pedigree. By using a combination of homozygosity mapping and positional candidate-gene screening, we identified a 2 bp deletion in LIPN that segregated with the disease phenotype throughout the family. LIPN encodes one of six acid lipases known to be involved in triglyceride metabolism in mammals . LIPN was found to be exclusively expressed in the epidermis and to be strongly induced during keratinocyte differentiation.