Revertant mosaicism in the skin.

Revertant mosaicism is a naturally occurring phenomenon involving the spontaneous correction of a pathogenic mutation in a somatic cell. Revertant mosaicism is not a rare event and has been described in several inherited skin conditions, including various subtypes of epidermolysis bullosa. The recognition of revertant mosaicism paves the way for revertant therapy which represents a potentially exciting "natural gene therapy" option for genetic disorders. The skin provides a useful model for studying revertant mosaicism because it is readily accessible and easy to examine. In this paper, we provide an overview of revertant mosaicism and its relevance in genetic skin disorders.

Recurrent heterozygous missense mutation, p.Gly573Ser, in the TRPV3 gene in an Indian boy with sporadic Olmsted syndrome.

Olmsted syndrome (OS) is a rare genodermatosis that is often difficult to diagnose because of clinical overlap with other disorders and its uncertain mode of inheritance. The molecular basis of OS was investigated in an Indian boy using comparative exome sequencing and Sanger sequencing data. Sequencing identified a G-to-A transition at position c.573 in the TRPV3 gene, producing the missense mutation p.Gly573Ser in the proband. This mutation was not identified in the mother. This study supports the recent finding of TRPV3 as the gene implicated in OS and suggests that the mutation p.Gly573Ser may be a recurrent abnormality in this genodermatosis.

MBTPS2 mutation in a British pedigree with keratosis follicularis spinulosa decalvans.

Keratosis follicularis spinulosa decalvans (KFSD; OMIM 308800) is an X-linked disorder characterized by widespread hyperkeratotic follicular papules (including keratosis pilaris-like lesions), facial erythema, hypotrichosis and scarring alopecia. KFSD results from mutations in the MBTPS2 gene. Mutations in this gene also underlie ichthyosis follicularis, alopecia and photophobia syndrome. We report a British pedigree with KFSD resulting from the mutation p.Asn508Ser. This particular mutation has been reported in three other pedigrees with KFSD (Dutch, American, British) and is the only pathogenic mutation reported in this disorder to date. However, the same mutation has also been reported in a Chinese pedigree with IFAP syndrome, highlighting the clinical heterogeneity and overlapping molecular pathology of these two disorders.

Mutations in AEC syndrome skin reveal a role for p63 in basement membrane adhesion, skin barrier integrity and hair follicle biology.

BACKGROUND: AEC (ankyloblepharon-ectodermal defects-clefting) syndrome is an autosomal dominant ectodermal dysplasia disorder caused by mutations in the transcription factor p63. Clinically, the skin is dry and often fragile; other features can include partial eyelid fusion (ankyloblepharon), hypodontia, orofacial clefting, sparse hair or alopecia, and nail dystrophy. OBJECTIVES: To investigate how p63 gene mutations affect gene and protein expression in AEC syndrome skin. METHODS: We performed microarray analysis on samples of intact and eroded AEC syndrome skin compared with control skin. Changes were verified by quantitative real-time reverse transcription-polymerase chain reaction and, for basal keratinocyte-associated genes, by immunohistochemistry and analysis of microdissected skin. RESULTS: We identified significant upregulation of six genes and downregulation of 69 genes in AEC syndrome skin, with the main changes in genes implicated in epidermal adhesion, skin barrier formation and hair follicle biology. There was reduced expression of genes encoding the basement membrane proteins FRAS1 and collagen VII, as well as the skin barrier-associated small proline-rich proteins 1A and 4, late cornified envelope protein 5A, hornerin, and lipid transporters including ALOX15B. Reduced expression of the hair-associated keratins 25, 27, 31, 33B, 34, 35, 81 and 85 was also noted. We also confirmed similar alterations in gene expression for 26 of the 75 genes in eroded AEC scalp skin. CONCLUSIONS: This study identifies specific changes in skin structural biology and signalling pathways that result from mutant p63 and provides new molecular insight into the AEC syndrome phenotype.

Infantile systemic hyalinosis associated with a putative splice-site mutation in the ANTXR2 gene.

Infantile systemic hyalinosis (ISH) is a rare autosomal recessive genetic disorder characterized by dermal and subcutaneous fibromatosis, joint contractures and bone deformities. The condition usually presents at birth, resulting in death in infancy. ISH is caused by mutations in the anthrax toxin receptor 2 gene, ANTXR2, also known as CMG2. We report an Indian child with ISH in whom we identified a homozygous acceptor splice site mutation, IVS2-4G>A. In silico analysis of this sequence showed that it changed predicted cryptic splicing, leading to out-of-frame transcripts and little, if any, functional protein. Mutations in the ANTXR2 gene can also cause juvenile hyaline fibromatosis (JHF). Although there are currently no effective treatments for ISH or JHF, identification of pathogenetic mutations in the ANTXR2 gene makes DNA-based prenatal diagnosis feasible for subsequent pregnancies.

New homozygous SPINK5 mutation, p.Gln333X, in a Turkish pedigree with Netherton syndrome.

Netherton syndrome (NS) is a rare autosomal recessive genodermatosis caused by loss-of-function mutations in the SPINK5 gene. The clinical features include congenital ichthyosis, trichorrhexis invaginata and atopy. In this study, we report a new homozygous SPINK5 mutation, p.Gln333X, responsible for NS in affected members of two closely related Turkish families, and provide an overview of the genotype-phenotype correlation in this condition.

The role of kindlins in cell biology and relevance to human disease.

The kindlins represent a class of focal adhesion proteins implicated in integrin activation. They comprise three evolutionarily conserved members, kindlin-1, kindlin-2 and kindlin-3, that share considerable sequence and structural similarities. The kindlins have a bipartite FERM (four point one protein, ezrin, radixin, moesin) domain interrupted by a pleckstrin homology domain and can bind directly to various classes of integrins as well as participate in inside-out integrin activation. They are encoded by three different genes, namely KIND1 (FERMT1; chromosome 20p12.3), KIND2 (FERMT2; chromosome 14q22.1) and KIND3 (FERMT3; chromosome 11q13.1). Loss-of-function mutations in KIND1 and KIND3 cause Kindler syndrome and leukocyte adhesion deficiency-III syndrome, respectively, although no human disease has yet been associated with KIND2 gene pathology. In this review, we focus on the cellular functions of the kindlins and their clinical relevance.

New insight into mechanisms of pruritus from molecular studies on familial primary localized cutaneous amyloidosis.

Macular and lichen amyloidosis are common variants of primary localized cutaneous amyloidosis (PLCA) in which clinical features of pruritus and skin scratching are associated with histological findings of deposits of amyloid staining on keratinous debris in the papillary dermis. Most cases are sporadic, but an autosomal dominant family history may be present in up to 10% of cases, consistent with a genetic predisposition in some individuals. Familial PLCA has been mapped to a locus on 5p13.1-q11.2 and in 2008 pathogenic heterozygous missense mutations were identified in the OSMR gene, which encodes oncostatin M receptor beta (OSMRbeta), an interleukin (IL)-6 family cytokine receptor. OSMRbeta is expressed in various cell types, including keratinocytes, cutaneous nerves and nociceptive neurones in dorsal root ganglia; its ligands are oncostatin M and IL-31. All pathogenic mutations are clustered in the fibronectin-III repeat domains of the extracellular part of OSMRbeta, sites that are critical for receptor dimerization (with either gp130 or IL-31RA), and lead to defective signalling through Janus kinase-signal transducers and activators of transcription, extracellular signal-regulated protein kinase 1/2 and phosphoinositide 3 kinase/Akt pathways. Elucidating the molecular pathology of familial PLCA provides new insight into mechanisms of pruritus in human skin, findings that may have relevance to developing novel treatments for skin itching. This review provides a clinicopathological and molecular update on familial PLCA.

Autosomal dominant junctional epidermolysis bullosa.

BACKGROUND: Epidermolysis bullosa (EB) encompasses a heterogeneous group of inherited skin disorders associated with trauma-induced blistering. The junctional forms of EB (JEB), Herlitz JEB, non-Herlitz JEB and JEB associated with pyloric atresia have all been attributed to autosomal recessive inheritance. We describe a 7-year-old girl with defective dental enamel, trauma-induced blistering and subsequent scarring. Her mother, a carrier of the mutation p.G627V in the collagen XVII gene (COL17A1) had evidence of hypoplastic dental enamel without skin blistering. Her grandmother had non-Herlitz JEB as a result of a compound heterozygous mutation in COL17A1 (p.G627V and c.3514ins25). OBJECTIVES: To explore the molecular, ultrastructural and immunofluorescence findings of the first case of dominant JEB. METHODS: Mutational analysis of COL17A1 was performed on the proband's genomic DNA. In addition, transmission electron microscopy and immunofluorescence microscopy were performed on a nonlesional skin biopsy from the proband and an unrelated healthy control. RESULTS: Direct sequencing revealed a heterozygous glycine substitution mutation, p.G627V, in COL17A1. No discernible morphological abnormalities were found on transmission electron microscopy; however, immunofluorescence microscopy revealed findings of an altered distribution pattern for type XVII collagen epitopes close to the dermal-epidermal junction. CONCLUSION: This report describes the first case of dominant JEB. Although some heterozygous mutations in COL17A1 are known to cause dental abnormalities none were associated with skin fragility. The dominant-negative interference between the proband's mutated type XVII collagen and the wild-type allele appears to render the skin prone to trauma-induced blister formation. Alternatively, other undisclosed modifying genetic or epigenetic factors might explain why the patient gets blistering whereas her mother, who has the same COL17A1 mutation, has no skin fragility.

Kindler syndrome: a focal adhesion genodermatosis.

Kindler syndrome (OMIM 173650) is an autosomal recessive genodermatosis characterized by trauma-induced blistering, poikiloderma, skin atrophy, mucosal inflammation and varying degrees of photosensitivity. Although Kindler syndrome is classified as a subtype of epidermolysis bullosa, it has distinct clinicopathological and molecular abnormalities. The molecular pathology of Kindler syndrome involves loss-of-function mutations in a newly recognized actin cytoskeleton-associated protein, now known as fermitin family homologue 1, encoded by the gene FERMT1. This protein mediates anchorage between the actin cytoskeleton and the extracellular matrix via focal adhesions, and thus the structural pathology differs from other forms of epidermolysis bullosa in which there is a disruption of the keratin intermediate filament-hemidesmosome network and the extracellular matrix. In the skin, fermitin family homologue 1 is mainly expressed in basal keratinocytes and binds to the cytoplasmic tails of beta1 and beta3 integrins as well as to fermitin family homologue 2 and filamin-binding LIM protein 1. It also plays a crucial role in keratinocyte migration, proliferation and adhesion. In this report, we review the clinical, cellular and molecular pathology of Kindler syndrome and discuss the role of fermitin family homologue 1 in keratinocyte biology.

Novel truncating mutations in PKP1 and DSP cause similar skin phenotypes in two Brazilian families.

Inherited mutations in components of desmosomes result in a spectrum of syndromes characterized by variable abnormalities in the skin and its appendages, including blisters and erosions, palmoplantar hyperkeratosis, woolly hair or hypotrichosis and, in some cases, extracutaneous features such as cardiomyopathy. We investigated the molecular basis of two Brazilian patients presenting with clinical features consistent with ectodermal dysplasia-skin fragility syndrome. In patient 1 we identified a homozygous nonsense mutation, p.R672X, in the PKP1 gene (encoding plakophilin 1). This particular mutation has not been reported previously but is similar to the molecular pathology underlying other cases of this syndrome. In patient 2 we found compound heterozygosity for two frameshift mutations, c.2516del4 and c.3971del4, in the DSP gene (encoding desmoplakin). Although there was considerable clinical overlap in the skin and hair abnormalities in these two cases, patient 2 also had early-onset cardiomyopathy. The mutation c.3971del4 occurs in the longer desmoplakin-I isoform (which is the major cardiac transcript) but not in the more ubiquitous desmoplakin-II. In contrast, PKP1 is not expressed in the heart, which accounts for the lack of cardiomyopathy in patient 1. Collectively, these cases represent the first desmosomal genodermatoses to be reported from Brazil and add to genotype-phenotype correlation in this group of inherited disorders. Loss-of-function mutations in the DSP gene can result in a phenotype similar to ectodermal dysplasia-skin fragility syndrome resulting from PKP1 mutations but only DSP pathology is associated with cardiac disease.

Colocalization of kindlin-1, kindlin-2, and migfilin at keratinocyte focal adhesion and relevance to the pathophysiology of Kindler syndrome.

Kindler syndrome (KS) results from pathogenic loss-of-function mutations in the KIND1 gene, which encodes kindlin-1, a focal adhesion and actin cytoskeleton-related protein. How and why abnormalities in kindlin-1 disrupt keratinocyte cell biology in KS, however, is not yet known. In this study, we identified two previously unreported binding proteins of kindlin-1: kindlin-2 and migfilin. Co-immunoprecipitation and confocal microscopy studies show that these three proteins bind to each other and colocalize at focal adhesion in HaCaT cells and normal human keratinocytes. Moreover, loss-of-function mutations in KIND1 result in marked variability in kindlin-1 immunolabeling in KS skin, which is mirrored by similar changes in kindlin-2 and migfilin immunoreactivity. Kindlin-1, however, may function independently of kindlin-2 and migfilin, as loss of kindlin-1 expression in HaCaT keratinocytes by RNA interference and in KS keratinocytes does not affect KIND2 or FBLIM1 (migfilin) gene expression or kindlin-2 and migfilin protein localization. In addition to identifying protein-binding partners for kindlin-1, this study also highlights that KIND1 gene expression and kindlin-1 protein labeling are not always reduced in KS, findings that are relevant to the accurate laboratory diagnosis of this genodermatosis by skin immunohistochemistry.

Unusual molecular findings in Kindler syndrome.

Kindler syndrome (KS) is a rare inherited skin disorder with blistering and poikiloderma as its main clinical features. It is caused by loss-of-function mutations in the C20orf42 (KIND1) gene which encodes kindlin-1, an actin cytoskeleton-focal contact-associated protein which is predominantly expressed in keratinocytes. We investigated the molecular basis of KS in a 16-year-old Indian boy who had additional clinical findings, including scleroatrophic changes of the hands and feet, pseudoainhum and early onset of squamous cell carcinoma on his foot. Immunostaining for kindlin-1 in the patient's skin was completely absent and sequencing of C20orf42 (KIND1) genomic DNA showed a homozygous splice-site mutation at the -6 position, IVS9-6T-->A. Amplification and sequencing of cDNA from the skin revealed aberrant splicing with either deletion of exon 10 or deletion of exons 9, 10 and 11, both of which involve loss of the pleckstrin homology domain of kindlin-1 that is thought to play a role in cytoskeletal attachment and integrin-mediated cell signalling. Pathogenic splice-site mutations at the -6 position are unusual and have rarely been reported for any genetic disorder. Collectively, these findings extend the spectrum of clinical and molecular abnormalities in this rare genodermatosis.