Ligneous conjunctivitis: Fresh-frozen plasma and heparin use intra-and postoperatively, a report of two cases

Ligneous conjunctivitis is a rare chronic form of recurrent membranous inflammation and plasminogen deficiency. Ocular manifestations may be associated with sites other than mucous membranes, such as the oral cavity, internal ear, respiratory, genitals, and kidney. Treatment is extremely difficult because of the lack of topic plasminogen drops, and a high volume is required for systemic supplementation. This report aimed to present two patients with ligneous conjunctivitis treated with membrane excision, topical fresh-frozen plasma, and heparin intra-, and postoperatively. No recurrence was found in the ligneous membrane in the 12-month follow-up. The use of topical fresh-frozen plasma and heparin after membrane excision could be effective to avoid recurrence.

X-linked genodermatoses from diagnosis to tailored therapy

Background

Genodermatoses are rare heterogeneous genetic skin diseases with multiorgan involvement. They severely impair an individual's well-being and can also lead to early death.

Methods

During the progress of this review, we have implemented a targeted research approach, diligently choosing the most relevant and exemplary articles within the subject matter. Our method entailed a systematic exploration of the scientific literature to ensure a compre-hensive and accurate compilation of the available sources.

Results

Among genodermatoses, X-linked ones are of particular importance and should always be considered when pediatric males are affected. Regardless of other syndromic forms without prevalence of skin symptoms, X-linked genodermatoses can be classified in three main groups: keratinization defects, pigmentation defects, and inflammatory skin diseases. Typical examples are dyskeratosis congenita, keratosis follicularis spinulosa decalvans, hypohidrotic ectodermal dysplasia, chondrodysplasia punctata, hypohidrotic ectodermal dysplasia, incontinentia pigmenti, chronic granulomatous disease, CHILD syndrome and ichthyosis. In this field, genetic diagnosis of the specific disease is important, also considering that numerous clinical trials of orphan drugs and genetic therapies are being proposed for these rare genetic diseases.

Conclusions

Thus, this chapter starts from clinical to molecular testing and ends with a review of all clinical trials on orphan drugs and gene therapy for genodermatoses.

Ex vivo gene modification therapy for genetic skin diseases-recent advances in gene modification technologies and delivery

Genetic skin diseases, also known as genodermatoses, are inherited disorders affecting skin and constitute a large and heterogeneous group of diseases. While genodermatoses are rare with the prevalence rate of less than 1 in 50,000 - 200,000, they frequently occur at birth or early in life and are generally chronic, severe, and could be life-threatening. The quality of life of patients and their families are severely compromised by the negative psychosocial impact of disease, physical manifestations, and the lack or loss of autonomy. Currently, there are no curative treatments for these conditions. Ex vivo gene modification therapy that involves modification or correction of mutant genes in patients' cells in vitro and then transplanted back to patients to restore functional gene expression has being developed for genodermatoses. In this review, the ex vivo gene modification therapy strategies for genodermatoses are reviewed, focusing on current advances in gene modification and correction in patients' cells and delivery of genetically modified cells to patients with discussions on gene therapy trials which have been performed in this area.

Is there a role for blood purification therapies targeting cytokine storm syndrome in critically severe COVID-19 patients?

The coronavirus disease-19 (COVID-19) has spread over many countries and regions since the end of 2019, becoming the most severe public health event at present. Most of the critical cases developed multiple organ dysfunction, including acute kidney injury (AKI). Cytokine storm syndrome (CSS) may complicate the process of severe COVID-19 patients. This manuscript reviews the different aspects of blood purification in critically ill patients with AKI and increased inflammatory factors, and examines its potential role in severe COVID-19 treatment. Continuous renal replacement therapy (CRRT) has been practiced in many sepsis patients with AKI. Still, the timing and dosing need further robust evidence. In addition to the traditional CRRT, the high-throughput membrane with adsorption function and cytokine adsorption column are two representatives of recently emerging novel membrane technologies. Their potential in removing inflammatory factors and other toxins prospects for the treatment of severe COVID-19.

Primary Localized Cutaneous Nodular Amyloidosis in the Absence of Systemic Disease

A 41-year-old man presented with an asymptomatic, slowly enlarging plaque on the lower aspect of his left cheek, present for approximately 4 months. His past medical history was remarkable for allergic rhinitis. Three years before, he had had a nearly identical lesion surgically excised by Mohs method at the same site. On examination, there was a waxy, yellowish plaque, measuring 2.1 cm × 1.0 cm on the left cheek in proximity to the oral commissure (Figure 1). A shave biopsy revealed an atrophic epidermis with nodular aggregates of eosinophilic material in the dermis (Figure 2). Higher magnification showed an inflammatory infiltrate composed largely of plasma cells, which stained positively for CD20 and κ light chains (Figure 3). Congo red staining confirmed the diagnosis of nodular amyloidosis (Figure 4).

Inactivating PTH/PTHrP Signaling Disorders

Pseudohypoparathyroidism (PHP), pseudo-PHP, acrodysostosis, and progressive osseous heteroplasia are heterogeneous disorders characterized by physical findings, differently associated in each subtype, including short bones, short stature, a stocky build, ectopic ossifications (features associated with Albright's hereditary osteodystrophy), as well as laboratory abnormalities consistent with hormone resistance, such as hypocalcemia, hyperphosphatemia, and elevated parathyroid hormone (PTH) and thyroid-stimulating hormone levels. All these disorders are caused by impairments in the cAMP-mediated signal transduction pathway and, in particular, in the PTH/PTHrP signaling pathway: the main subtypes of PHP and related disorders are caused by de novo or autosomal dominantly inherited inactivating genetic mutations, and/or epigenetic, sporadic, or genetic-based alterations within or upstream of GNAS, PRKAR1A, PDE4D, and PDE3A. Here we will review the impressive progress that has been made over the past 30 years on the pathophysiology of these diseases and will describe the recently proposed novel nomenclature and classification. The new term "inactivating PTH/PTHrP signaling disorder," iPPSD: (1) defines the common mechanism responsible for all diseases, (2) does not require a confirmed genetic defect, (3) avoids ambiguous terms like "pseudo," and (4) eliminates the clinical or molecular overlap between diseases.

Annular Lesions: Diagnosis and Treatment

Annular lesions can present in a variety of diseases. Knowledge of the physical appearance and history of presentation of these skin findings can help in the diagnosis. A pruritic, annular, erythematous patch that grows centrifugally should prompt evaluation for tinea corporis. Tinea corporis may be diagnosed through potassium hydroxide examination of scrapings. Recognizing erythema migrans is important in making the diagnosis of Lyme disease so that antibiotics can be initiated promptly. Plaque psoriasis generally presents with sharply demarcated, erythematous silver plaques. Erythema multiforme, which is due to a hypersensitivity reaction, presents with annular, raised lesions with central clearing. Lichen planus characteristically appears as planar, purple, polygonal, pruritic papules and plaques. Nummular eczema presents as a rash composed of coin-shaped papulovesicular erythematous lesions. Treatment is aimed at reducing skin dryness. Pityriasis rosea presents with multiple erythematous lesions with raised, scaly borders, and is generally self-limited. Urticaria results from the release of histamines and appears as well-circumscribed, erythematous lesions with raised borders and blanched centers. Annular lesions occur less commonly in persons with fixed drug eruptions, leprosy, immunoglobulin A vasculitis, secondary syphilis, sarcoidosis, subacute cutaneous lupus erythematosus, and granuloma annulare.

Treatment of Ligneous Conjunctivitis Using Topical Plasminogen Therapy in an 8-Week-Old Female Infant

An 8-week-old female infant presented with bilateral eyelid swelling and conjunctival membranes. She was diagnosed as having ligneous conjunctivitis. The membranes were excised but recurred despite topical cyclosporine, heparin, fresh frozen plasma, and systemic fresh frozen plasma transfusions. Topical plasminogen prevented membrane recurrence and intravenous plasminogen therapy treated systemic manifestations of the disease. [J Pediatr Ophthalmol Strabismus. 2018;55:e30-e32.].

Acquired and congenital forms of heterotopic ossification: new pathogenic insights and therapeutic opportunities

Heterotopic ossification (HO) involves the formation and accumulation of extraskeletal bone tissue at the expense of local tissues including muscles and connective tissues. There are common forms of HO that are triggered by extensive trauma, burns and other bodily insults, and there are also rare congenital severe forms of HO that occur in children with Fibrodysplasia Ossificans Progressiva or Progressive Osseous Heteroplasia. Given that HO is often preceded by inflammation, current treatments usually involve anti-inflammatory drugs alone or in combination with local irradiation, but are not very effective. Recent studies have provided novel insights into the pathogenesis of acquired and genetic forms of HO and have used the information to conceive and test new and more specific therapies in animal models. In this review, I provide salient examples of these exciting and promising advances that are undoubtedly paving the way toward resolution of this debilitating and at times fatal disease.

RNA-based therapies for genodermatoses

Genetic disorders affecting the skin, genodermatoses, constitute a large and heterogeneous group of diseases, for which treatment is generally limited to management of symptoms. RNA-based therapies are emerging as a powerful tool to treat genodermatoses. In this review, we discuss in detail RNA splicing modulation by antisense oligonucleotides and RNA trans-splicing, transcript replacement and genome editing by in vitro-transcribed mRNAs, and gene knockdown by small interfering RNA and antisense oligonucleotides. We present the current state of these therapeutic approaches and critically discuss their opportunities, limitations and the challenges that remain to be solved. The aim of this review was to set the stage for the development of new and better therapies to improve the lives of patients and families affected by a genodermatosis.

A 7-year-old with indurated skin and unilateral progressive joint immobility: A case of stiff skin syndrome

Stiff skin syndrome is a rare sclerotic condition that presents during infancy or early childhood. It has an insidious chronic course and may lead to significant co-morbidity and reduced quality of life. Often, affected individuals experience impaired ambulation and immobilization related to joint involvement. Clinically, it may resemble other sclerotic diseases, so histopathological evaluation is necessary to establish a diagnosis. As it is a condition with limited treatment options, prompt diagnosis and early initiation of physical therapy is crucial to prevent joint restriction and maintain quality of life. We describe a case of a 7-year-old with stiff skin syndrome, and review the literature to discuss the clinical presentation, histological findings, and management of this condition.

Primary scarring alopecias

Scarring alopecia or cicatricial alopecia results from follicular damage that is sufficient to cause the destruction and replacement of pilosebaceous structures by scar tissue. Primary scarring alopecias represent a group of disorders that primarily affect the hair follicles, as opposed to secondary scarring alopecias, which affect the dermis and secondarily cause follicular destruction. Inflammation may predominantly involve lymphocytes or neutrophils. Cicatricial alopecias that mainly involve lymphocytic inflammation include discoid lupus erythematosus, lichen planopilaris, frontal fibrosing alopecia, central centrifugal alopecia, and pseudopelade (Brocq). Cicatricial alopecias that are due to predominantly neutrophilic inflammation include folliculitis decalvans, tufted folliculitis, and dissecting cellulitis of the scalp. Folliculitis keloidalis is a cicatricial alopecia with a mixed inflammatory infiltrate.

Dissecting cellulitis (Perifolliculitis Capitis Abscedens et Suffodiens): a comprehensive review focusing on new treatments and findings of the last decade with commentary comparing the therapies and causes of dissecting cellulitis to hidradenitis suppurativa

Dissecting cellulitis (DC) also referred to as to as perifolliculitis capitis abscedens et suffodiens (Hoffman) manifests with perifollicular pustules, nodules, abscesses and sinuses that evolve into scarring alopecia. In the U.S., it predominantly occurs in African American men between 20-40 years of age. DC also occurs in other races and women more rarely. DC has been reported worldwide. Older therapies reported effective include: low dose oral zinc, isotretinoin, minocycline, sulfa drugs, tetracycline, prednisone, intralesional triamcinolone, incision and drainage, dapsone, antiandrogens (in women), topical clindamycin, topical isotretinoin, X-ray epilation and ablation, ablative C02 lasers, hair removal lasers (800nm and 694nm), and surgical excision. Newer treatments reported include tumor necrosis factor blockers (TNFB), quinolones, macrolide antibiotics, rifampin, alitretinoin, metronidazole, and high dose zinc sulphate (135-220 mg TID). Isotretinoin seems to provide the best chance at remission, but the number of reports is small, dosing schedules variable, and the long term follow up beyond a year is negligible; treatment failures have been reported. TNFB can succeed when isotretinoin fails, either as monotherapy, or as a bridge to aggressive surgical treatment, but long term data is lacking. Non-medical therapies noted in the last decade include: the 1064 nm laser, ALA-PDT, and modern external beam radiation therapy. Studies that span more than 1 year are lacking. Newer pathologic hair findings include: pigmented casts, black dots, and "3D" yellow dots. Newer associations include: keratitis-ichthyosis-deafness syndrome, Crohn disease and pyoderma gangrenosum. Older associations include arthritis and keratitis. DC is likely a reaction pattern, as is shown by its varied therapeutic successes and failures. The etiology of DC remains enigmatic and DC is distinct from hidradenitis suppurativa, which is shown by their varied responses to therapies and their histologic differences. Like HS, DC likely involves both follicular dysfunction and an aberrant cutaneous immune response to commensal bacteria, such as coagulase negative staphylococci. The incidence of DC is likely under-reported. The literature suggests that now most cases of DC can be treated effectively. However, the lack of clinical studies regarding DC prevents full understanding of the disease and limits the ability to define a consensus treatment algorithm.

Primary localized cutaneous nodular amyloidosis of the feet: a case report and review of the literature

Primary localized cutaneous nodular amyloidosis (PLCNA) is a rare disorder that manifests as the cutaneous formation of nodules composed of light-chain amyloid. Although the type of amyloid deposit is similar to primary systemic amyloidosis, there seems to be little, if any, crossover between the 2 diseases. Because reports of PLCNA are sparse, there is no established protocol for treating this disease. This case report presents a 42-year-old man with a visually striking presentation of PLCNA on both feet with some of the lesions possibly being secondary to trauma, a rare phenomenon. The lesions had been present for more than 4 years, and there were no signs or symptoms of systemic amyloidosis. The lesions responded well to a combination of complete curettage followed by CO2; laser ablation. Primary localized cutaneous nodular amyloidosis is rare and difficult to treat, with high rates of recurrence and a concern for progression to systemic amyloidosis. The diagnosis, workup, treatment, and monitoring of PLCNA also are discussed.

Stiff skin syndrome and myeloma successfully treated with autologous haematopoietic stem cell transplantation (HSCT)

Stiff skin syndrome (SSS) is a rare scleroderma-like syndrome characterised by stone hard skin, joint limitation and progressive restriction of chest that may lead to death. We describe the efficacy of haematopoietic autologous stem cell transplantation (HSCT) in a case of SSS secondary to a smouldering myeloma (SM), with severe joint disability, lung interstitial disease and oesophageal dysfunction. The patient was evaluated at 1, 12 and 18 months after HSCT, clinically (joint motility, HAQ and NYHA for dyspnoea) and instrumentally (DLCO, chest HRCT, oesophagus x-ray). After 18 months since HSCT, we observed a high improvement, contemporaneously to SM remission, of HAQ, joint motility, lung (at DLCO and HRCT) and oesophageal abnormalities.

Department-related tasks and organ-targeted therapy in Fabry disease: an interdisciplinary challenge

Fabry disease is a rare X-linked storage disorder leading to an accumulation of globotriaosylceramides in all cells carrying lysosomes. As the accumulation occurs in most organs, different medical specialties are involved in the diagnostics and therapy of Fabry disease. With this review of the 3 main specialties (cardiology, nephrology, and neurology) and, in addition, the adjacent specialties (ophthalmology and dermatology), we aim to discuss the division-related responsibilities and want to suggest an organ-related additional therapy besides enzyme replacement therapy.

Progress in heritable skin diseases: translational implications of mutation analysis and prospects of molecular therapies*

Epidermolysis bullosa, a group of blistering disorders, serves as the paradigm of the tremendous progress made in understanding the molecular genetics of heritable skin diseases. Mutations in 10 distinct genes have been disclosed in the classic forms of epidermolysis bullosa, and the level of expression of the mutated genes within the cutaneous basement membrane zone, the types and combinations of mutations and their consequences at the mRNA and protein levels, when placed in the context of the individual's genetic background and exposure to environmental trauma, all determine the subtype and the phenotypic severity in each case. The translational implications of mutation analysis include improved diagnosis and subclassification, refined genetic counseling of families at risk, and development of DNA-based pre natal and preimplantation genetic diagnosis. The prospects of molecular therapies for epidermolysis bullosa include further development of strategies for gene therapy, protein replacement therapy and cell-based therapies, including stem cell therapy and bone marrow transfer. Collectively, advances in the molecular genetics of heritable skin diseases clearly emphasize the value of basic research for improved diagnostics and patient care for genetic skin diseases.

Cutaneous gene delivery

Over the past decade, many approaches to transferring genes into the skin have been investigated. However, most such approaches have been specifically aimed against genodermatosis, and have not produced sufficient results. The goal of such research is to develop a method in which genes are transferred easily, efficiently and stably into keratinocytes, especially into keratinocyte stem cells, and in which the transgene expression persists without a reaction from the host immune response. Although accidental development of cancer has occurred in trials of gene therapy for X-linked severe combined immunodeficiency (X-SCID), resulting in slowing of the progress of this research, the lessons of these setbacks have been applied to further research. Moreover, combined with the techniques acquired from tissue engineering, recent developments in our knowledge about stem cells will lead to new treatments for genodermatoses. The present review summarizes the methods by which therapeutic genes can be transferred into keratinocytes, with discussion of how gene transfer efficiency can be improved, with particular emphasis on disruption of the skin barrier function. It concludes with discussion of the challenges and prospects of keratinocyte gene therapy, in terms of achieving efficient and long-lasting therapeutic effects.

Cutaneous gene therapy

Possibilities of using the skin for somatic gene therapy have been investigated for more than 20 years. Strategies have included both direct gene transfer into the skin and indirect gene transfer utilizing cultured cells as an intermediate step for gene manipulation. Viral as well as nonviral vectors have been used, and both gene addition and gene editing have been performed. Although cutaneous gene therapy has now begun translating into clinical medicine (as seen by the first clinical gene therapy project of an inherited skin disorder) further developments are still required.

Molecular basis of inherited skin-blistering disorders, and therapeutic implications

Epidermolysis bullosa (EB) and associated skin-fragility syndromes are a group of inherited skin diseases characterised by trauma-induced blistering of the skin and mucous membranes. Mutations in at least 14 distinct genes encoding molecular components of the epidermis or the dermal–epidermal junction (DEJ) can cause blistering skin diseases that differ by clinical presentation and severity of the symptoms. Despite great advances in discerning the genetic basis of this group of diseases, the molecular pathways leading to symptoms are not yet fully understood. Unravelling these pathways by molecular analysis of the structure and in vitro assessment of functional properties of the human proteins involved, combined with genetic models in lower organisms, should pave the way for specific cures for inherited skin fragility.

Erythrokeratodermas: A classification in a state of flux?

The term 'erythrokeratodermas' or 'erythrokeratodermias' has been applied to a group of inherited disorders characterized by well-demarcated erythematous lesions and hyperkeratotic plaques. Connexin mutations have been demonstrated to be responsible for most cases of erythrokeratoderma variabilis but there remain some cases without demonstrated connexin mutations, suggesting genetic heterogeneity. The position of progressive symmetric erythrokeratoderma has become rather unclear. Loricin mutations have been found in some cases that clinically resemble variant Vohwinkel syndrome and other cases have features that overlap with those of erythrokeratoderma variablis. Whether progressive symmetric erythrokeratoderma exists as a distinct entity is under question.

Selected disorders of connective tissue: pseudoxanthoma elasticum, cutis laxa, and lipoid proteinosis

There has been progress made in the understanding of 3 Mendelian disorders: pseudoxanthoma elasticum, cutis laxa, and lipoid proteinosis cutis and mucosae. While they are primary connective tissue diseases, their names imply a connection to the skin, and in fact, it is often the dermatologist who makes the diagnosis. It seems rational that defects in various extracellular matrix proteins cause lipoid proteinosis or subtypes of cutis laxa, yet the discovery of a liver- and kidney-based transmembrane transporter as the culprit of pseudoxanthoma elasticum was rather surprising and may shed new light on elastic tissue homeostasis.

Gene therapy and the skin

Significant progress has been made during the past decade in corrective gene therapy of the skin. This includes advances in vector technology, targeted gene expression, gene replacement, gene correction, and the availability of appropriate animal models for a variety of candidate diseases. While non-viral integration of large genes such as essential basement membrane proteins has been mastered, new challenges such as the control of immune responses lie ahead of the research community. Among the first skin diseases, patients with junctional epidermolysis bullosa (JEB) and xeroderma pigmentosum (XP) will enter clinical trials.

RETRACTED: Progress and prospects of skin gene therapy: a ten year history

Significant progress has been made in corrective gene therapy of the skin in the last decade. This includes advances in vector technology, targeted gene expression, gene replacement, gene correction, and the availability of appropriate animal models for a variety of candidate diseases. While non-viral integration of large genes such as essential basement membrane proteins has been mastered, new challenges such as the control of immune responses lie ahead of the research community until skin gene therapy will become clinical reality. Among the first skin diseases patients with junctional epidermolysis bullosa and xeroderma pigmentosum have entered clinical trials.

Genetic immunodeficiency disorders

In this review, selected immunodeficiency disorders are presented in which the cutaneous signs are distinctive and contribute to the diagnosis of the condition. Among these cutaneous abnormalities are alopecia, cutaneous granulomas, cutaneous infections, atopic-like or seborrheic-like dermatitis, petechiae or purpura, silvery pigmentation, poor wound healing, and telangiectasias. Immunodeficiency should be considered in children with a history of infections that are recurrent, respond poorly to antibiotics, are of increased duration and severity, and/or result from unusual organisms. In addition to their high risk of infection, patients with immunodeficiency disorders have a risk of the development of malignancy that is 10,000 times higher than that of healthy age-matched controls. The underlying molecular basis for most genetic immunodeficiencies is now understood, allowing improved genetic counseling and prenatal diagnosis.

Inducible Mouse Models for Inherited Skin Diseases: Implications for Skin Gene Therapy

Stem cells are crucial for the formation and maintenance of tissues and organs. To understand the role of stem cells in the pathogenesis of mosaic skin disorders, we generated inducible mouse models for two autosomal dominant keratin disorders, epidermolytic hyperkeratosis (EHK) and epidermolysis bullosa simplex (EBS), that enable activation of the respective mutation in epidermal stem cells in a spatially and temporally controlled manner using a ligand-inducible Cre recombinase. Whereas mosaic forms have been reported for EHK, which is caused by mutations in the suprabasal keratins K1 or K10, this has never been reported for EBS, which is due to mutations in the basal keratins K5 or K14. When we induced the phenotype in these models by topical application of the inducer, we found phenotypic areas in the EHK model that persisted for the life of the mouse. On the contrary, the induced blisters in the EBS model healed within a few weeks by migration of surrounding non-phenotypic stem cells into the wound bed. Our results indicate that lack of selective pressure against certain mutations in epidermal stem cells could explain why mosaic forms exist for EHK, but not for EBS. These findings have important implications for the development of new strategies for somatic gene therapy of dominant genodermatoses, and we are currently using these inducible mouse models to test gene therapy approaches.

[Hereditary blistering disorders]

Epidermolysis bullosa (EB) is a group of genetic skin disorders whose common feature is the formation of blisters following minor trauma. They present with a wide clinical spectrum of manifestations because of a variety of molecular defects. In patients with mild phenotypes, only skin is affected. The most severe EB forms are multiorgan disorders with a poor prognosis. EB arises from abnormalities in proteins of the dermal-epidermal junction. These specialized protein components aggregate to form anchoring complexes, which attach the epidermis to the dermis. Three major EB-forms can be distinguished on the basis of ultrastructural blistering level: EB simplex--epidermolytic, junctional EB--in the lamina lucida and dystrophic EB--dermolytic. To establish a provisional diagnosis for an EB patient, clinical data, family history and morphologic examination of the skin, e.g. by antigen-mapping, are needed. Complete knowledge of the genetic defect provides the basis to a rational genetic counseling and prenatal testing. Treatment of EB is based on wound care; multidisciplinary management of cases with severe course is required.

Erythrokeratoderma variabilis

Erythrokeratoderma variabilis is a rare autosomal dominant genodermatosis of variable expressivity. In this report, we describe the clinical features and microscopic findings in one of our patients born to unaffected parents. We also briefly review the literature on this disorder.

Natural repair mechanisms in correcting pathogenic mutations in inherited skin disorders

This review assesses molecular aspects of the rescue of disease-causing mutations in genodermatoses by means of naturally occurring secondary genetic phenomena. Such data have important implications for the design of gene therapy approaches for inherited skin diseases. Reversal of the phenotype depends on three elements: the number of cells involved; the degree of gene reversal; and the specific timing of the reversion. If reversion occurs in somatic cells, revertant mosaicism may occur. This is the situation in which a patient's skin is generally affected by the genodermatosis, but islands of normal skin stand out. These reflect the presence of revertant cells that are sufficient to restore a normal local skin phenotype. Reversion of the original mutation may also be partial, in which case the phenotype may display no, or only limited, improvement. Nevertheless, the phenotype may ameliorate with age if the reverted cells preferentially expand in time or if the time of onset of reversion is after birth. In essence, the complexities of naturally occurring rescue processes are important to understand because the inherent mechanisms may provide clues and insight into optimal therapeutic gene manipulation, and the possibility of mimicking nature in the management of patients with diverse genodermatoses.

Development of spliceosome-mediated RNA trans-splicing (SMaRT) for the correction of inherited skin diseases

Gene therapy of large genes (e.g. plectin and collagen genes) is hampered by size limitations for insertions of the currently used viral vectors. To reduce the size of these insertions spliceosome-mediated RNA trans-splicing (SMaRT), which provides intron-specific gene-correction at the pre-RNA level, can be an alternative approach. To test its applicability in skin gene therapy, SMaRT was used in the context of the 4003delTC mutation in the collagen XVII gene (COL17A1) causing generalized atrophic benign junctional epidermolysis bullosa. A beta-galactosidase (beta-gal) trans-splicing assay system was established using intron 51 of COL17A1 as the target for trans-splicing. In this system, intron 51 is flanked by the 5'exon and the 3'exon of the beta-gal gene, the latter containing two in-frame stop codons. Cotransfection of a pre-trans-splicing molecule consisting of the binding domain of intron 51 and the 3'exon of beta-gal without the stop codons resulted in a 300-fold increase of beta-gal activity compared to controls. A 2-3-fold increase in efficiency was obtained through an elongation of the binding domains. Replacement of the complete 3'end of the COL17A1 gene was shown using a collagen XVII mini-gene construct. The beta-gal assay was used in human keratinocytes to evaluate the influence of a keratinocyte-specific spliceosome background. Reverse transcription polymerase chain reaction and beta-gal activity assay showed functional correction of the stop-codons in cultured human keratinocytes and in an immortalized GABEB cell line harbouring the 4003delTC mutation. These results demonstrate that SMaRT is feasible in a keratinocyte-specific context and therefore may be applied in skin gene therapy.

The molecular genetics of the genodermatoses: progress to date and future directions

The Human Genome Mapping Project and allied rapid advances in genetic technology over the past decade have facilitated accurate association of allelic variations in several genes with specific skin phenotypes. Currently the genetic bases of the majority of the more common genodermatoses have been elucidated. In scientific terms this work has been extraordinarily successful and has yielded many new biological insights. These advances, although exciting, have yet to be translated into direct benefit for patients with these diseases. Genetic counselling has been greatly aided by gene identification, by the better understanding of genotype-phenotype correlation and by the disclosure of unexpected genetic mechanisms in some families. Knowledge of the molecular basis of these disorders has also been vital in enabling DNA-based prenatal diagnosis in several conditions and DNA-based preimplantation diagnosis has been used in a selected few. While this successful period of gene mapping is now nearing completion, progress towards the next goal, that of developing therapeutic strategies based on the knowledge of these underlying genetic mechanisms, has proven frustratingly slow. Despite the ready access to the skin compared with solid internal organs, the challenges of cutaneous gene therapy are legion and many technical issues need to be surmounted to enable gene replacement or modification of gene expression to have a useful role in these disorders. In this article we make a comprehensive review of progress to date in gene identification, genotype-phenotype correlation, prenatal diagnosis and cutaneous gene therapy, and we examine future directions for research in this field.

Xeroderma pigmentosum

Xeroderma pigmentosum is a rare disorder transmitted in an autosomal recessive manner. Xeroderma pigmentosum is based on a genetic defect in the DNA repair system. This disease manifests in early childhood. Patients with xeroderma pigmentosum have a marked sensitivity to sunlight and develop serious sunburns with onset of poikilodermia in the light-exposed skin. Squamous cell carcinomas, basal cell carcinomas and malignant melanomas already appear in childhood. The majority of patients die before reaching adulthood because of metastases. Genetically, xeroderma pigmentosum is divided into 7 complementation groups (XP-A to XP-G) and the xeroderma pigmentosum variants (XP-V). Diagnostically, assignment to the specific complementation group is made according to the fusioning of xeroderma pigmentosum fibroblasts. Differential diagnosis must distinguish xeroderma pigmentosum from other so-called DNA-repair-deficiency syndromes like the Cockayne Syndrome and trichothiodystrophy. Currently, there are reports of successful application of a topical DNA Repair Enzyme. This is a recombinant liposomal encapsulated T4 endonuclease V, which repairs UV-induced cyclobutan-pyrimidine dimers. In future, causal therapy could be based on gene therapy. The introduction of an intact repair gene which specifically codes the repair protein, could open new possibilities in the treatment of xeroderma pigmentosum.

Genetic reversion of inherited skin disorders

Human epidermis is a squamous stratified epithelium whose integrity relies on balanced processes of cell attachment, proliferation, and differentiation. In monogenic skin dermatoses, such as mecano-bullous diseases, or DNA repair deficiencies such as the xeroderma pigmentosum (XP), alterations of skin integrity may have devastating consequences as illustrated by the extremely high epidermal cancer proneness of XP patients. The lack of efficient pharmacological treatments, the easy accessibility of skin, and the possibility of long term culture and genetic manipulations ex vivo of epidermal keratinocytes, have encouraged approaches toward gene transfer and skin therapy prospects. We review here some of the human genetic disorders that exhibit major traits in skin, as well as requirements and difficulties inherent to approaches aimed at stable phenotypic correction.