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Clinical features indicative of revertant mosaicism in KS. (A-C) P1 exhibited numerous normal-appearing skin patches of several mm 2 to 15 cm 2 on the entire integument, which remained constant over the 3-year observation period. Shown are the right axilla, upper thorax, and right arm (A); the left arm (B); and the left leg (C). (D and E) P2 had normal-appearing skin patches on the right hand (D) and the right lower leg (E). Revertant areas investigated here are outlined in black; biopsy sites are circled in blue or directly visible.
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Spontaneous gene repair, also called revertant mosaicism, has been documented in several genetic disorders involving organs that undergo self-regeneration, including the skin. Genetic reversion may occur through different mechanisms, and in a single individual, the mutation can be repaired in various ways. Here we describe a disseminated pattern of...
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Context 1
... both patients had FERMT1 duplica- tion insertion mutations, which led to frame shifts, premature ter- mination codons, and loss of full-length kindlin-1, as demonstrated by immunoblotting of keratinocyte lysates (10). A systematic review of 24 additional KS patients revealed that all individuals harboring duplicating insertions (P3-P6; Table 1) exhibited the same skin pat- tern ( Supplemental Figures 1 and 2; supplemental material avail- able online with this article; doi:10.1172/JCI61976DS1). P1 and P2 were available for systematic investigation. ...
Context 2
... a 29-year-old male born to consanguineous parents, was homozygous for c.456dupA (11). During a 3-year follow-up, we noted normal-appearing patches with preserved texture, measur- ing between several mm 2 and 15 cm 2 , disseminated over the entire integument, that contrasted the atrophic, dry, hyperpigmented, and often erythematous skin (Figure 1, A-C). Immunofluorescence staining of a skin sample obtained from an atrophic area (P1-1) revealed absence of kindlin-1 at the DEJ ( Figure 2B). ...
Context 3
... a 24-year-old female homozygous for c.676dupC, exhib- ited multiple normal-appearing patches, measuring 0.5-2 cm 2 , that were clearly distinguishable from the atrophic integument ( Figure 1, D and E). Kindlin-1 immunofluorescence was nega- tive in the affected skin, but positive (comparable to control skin) in 2 normal-appearing patches (Figure 2, D and E, and Supplemental Table 1). ...
Citations
... At the time of the initial description of RM in a genodermatosis in 1997, RM was considered an extraordinary phenomenon. However, since that initial description, RM has been identified in all major types of EB (Table 1) [63][64][65][66][67][68][69][70][71][72][73][74][75][76][77][78], and, in 2012, we were able to confirm revertant skin patches in all ten Dutch patients with the intermediate type of JEB due to pathogenic COL17A1 variants [79]. Around the same time, Choate et al. demonstrated that each of the multiple healthy 'confetti-like' spots in patients with ichthyosis with confetti (IWC) due to germline variants in KRT10 (IWC-I) or KRT1 (IWC-II) represent a separate occurrence of RM in a single keratinocyte clone [80,81]. ...
... The reason why RM is frequently seen in skin likely has to do with the facts that skin can easily be explored visually and is a rapidly self-renewing organ in which a large number of cell divisions take place, which means it is analogous to bone marrow and the frequent occurrence of RM observed in hematologic and immunologic disorders (Supplementary Table S1). [86], (e) the severe type of generalized recessive dystrophic epidermolysis bullosa (RDEB-gen, COL7A1) [68], (f) Kindler epidermolysis bullosa (Kindler EB, FERMT1) [70], (g) ichthyosis with confetti type 1 (IWC-I, KRT10) [81], (h) ichthyosis with confetti type 2 (IWC-II, KRT1) [87], (i) loricrin keratoderma (LK, LOR) [83], (j) keratitis-ichthyosis-deafness syndrome (KID, GJB2), and (k) pityriasis rubra pilaris (PRP, CARD14) [84]. Solid or dashed lines indicate revertant patches amidst affected skin (note that on several panels more revertant patches are visible than highlighted). ...
... Of note, in the cases with presumed back-mutations, it was not always possible to distinguish a back-mutation from a mitotic recombination event [75,86]. Other somatic, small intragenic mutational events that have been reported are deletions or duplications of one or a few nucleotides that either directly restore a disturbed mutant reading frame or modify mutant splicing patterns and thereby restore mutant reading frames [69][70][71]73,78,79]. Such correction events were observed frequently in Kindler EB as certain repetitive nucleotide sequences in FERMT1 appear to be particularly prone to the duplication or deletion of single nucleotides due to slipped mispairing [69,70]. ...
Revertant mosaicism (RM) is the intriguing phenomenon in which nature itself has successfully done what medical science is so eagerly trying to achieve: correcting the effect of disease-causing germline variants and thereby reversing the disease phenotype back to normal. RM was molecularly confirmed for the first time in a genodermatosis in 1997, the genetic skin condition junctional epidermolysis bullosa (EB). At that time, RM was considered an extraordinary phenomenon. However, several important discoveries have changed this conception in the past few decades. First, RM has now been identified in all major subtypes of EB. Second, RM has also been identified in many other genodermatoses. Third, a theoretical mathematical exercise concluded that reverse mutations should be expected in all patients with a recessive subtype of EB or any other genodermatosis. This has shifted the paradigm from RM being an extraordinary phenomenon to it being something that every physician working in the field of genodermatoses should be looking for in every patient. It has also raised hope for new treatment options in patients with genodermatoses. In this review, we summarize the current knowledge on RM and discuss the perspectives of RM for the future treatment of patients with genodermatoses.
... Following PCR amplification, haplotype, and direct sequencing, researchers concluded that COL17A1 gene conversion-nonreciprocal transfer at a specific gene locus where part of an allele was replaced by the homologous segment from another allele-was the most likely mechanism. RM has since been documented in EBS, JEB generalized intermediate, RDEB, DDEB, and Kindler syndrome, implicating COL17A1, KRT14, LAMB3, COL7A1, and FERMT1 genes [15][16][17][18][19][20][21][22][23][24][25][26][27][28] (Figure 2, Table 1), and the topic of prior reviews [19,29,30]. Clinically, patches of revertant mosaic keratinocytes in COL17A1 are identifiable as relatively hyperpigmented patches of skin compared to the surrounding affected epidermis [31]. ...
Epidermolysis bullosa (EB) is a group of genetic blistering diseases characterized by mechanically fragile skin and mucocutaneous involvement. Historically, disease management has focused on supportive care. The development of new genetic, cellular, and recombinant protein therapies has shown promise, and this review summarizes a unique gene and cell therapy phenomenon termed revertant mosaicism (RM). RM is the spontaneous correction of a disease-causing mutation. It has been reported in most EB subtypes, some with relatively high frequency, and has been observed in both keratinocytes and fibroblasts. RM manifests as identifiable patches of unaffected, blister-resistant skin and can occur through a variety of molecular mechanisms, including true back mutation, intragenic crossover, mitotic gene conversion, and second-site mutation. RM cells represent a powerful autologous platform for therapy, and leveraging RM cells as a therapeutic substrate may avoid the inherent mutational risks of gene therapy/editing. However, further examination of the genomic integrity and long-term functionality of RM-derived cells, as well in vivo testing of systemic therapies with RM cells, is required to realize the full therapeutic promise of naturally occurring RM in EB.
... A naturally occurring phenomenon known as revertant mosaicism has been harnessed as a form of gene therapy in RDEB. This refers to the spontaneous conversion of a mutated somatic cell acquiring a second mutation to self-correct its condition, producing clinically normal patches of skin, as is frequently observed in genetic skin conditions, 42 including RDEB 43 and Kindler EB. 44 Researchers have attempted to generate induced pluripotent stem cells (iPSCs) from clinically normal skin of patients with RDEB to generate naturally genecorrected RDEB keratinocytes that can be grafted onto wound sites. [45][46][47][48] iPSCs can be produced from any somatic cell (e.g. ...
Epidermolysis bullosa (EB) encompasses a heterogeneous group of inherited skin fragility disorders with mutations in genes encoding the basement membrane zone (BMZ) proteins that normally ensure dermal-epidermal integrity. Of the four main EB types, recessive dystrophic EB (RDEB), especially the severe variant, represents one of the most debilitating clinical entities with recurrent mucocutaneous blistering and ulceration leading to chronic wounds, infections, inflammation, scarring and ultimately cutaneous squamous cell carcinoma, which leads to premature death. Improved understanding of the molecular genetics of EB over the past three decades and advances in biotechnology has led to rapid progress in developing gene and cell-based regenerative therapies for EB. In particular, RDEB is at the vanguard of advances in human clinical trials of advanced therapeutics. Furthermore, the past decade has witnessed the emergence of a real collective, global effort involving academia and industry, supported by international EB patient organisations such as the Dystrophic Epidermolysis Bullosa Research Association (DEBRA), amongst others, to develop clinically relevant and marketable targeted therapeutics for EB. Thus, there is an increasing need for the practising dermatologist to become familiar with the concept of gene therapy, fundamental differences between various approaches and their human applications. This review explains the principles of different approaches of gene therapy; summarises its journey and discusses its current and future impact in RDEB.
... How kindlins act is less well-de ned, while diseasecausing mutations show that kindlins are essential for integrin activation, adhesion, cell spreading and signaling [5]. Kiritsi et al has reported that the restoration of kindlin-1 led to structurally normal skin, while loss of kindlin-1 severely impaired keratinocyte proliferation [6]. Loss of kindlin-1 in mouse keratinocytes recapitulates KNDLRS and produces enlarged and hyperactive stem cell compartments, which lead to hyperthickened epidermis, ectopic hair follicle development and increased skin tumor susceptibility [7]. ...
Background: Kindler syndrome (KNDLRS) is a very rare autosomal recessive disorder characterized by bullous poikiloderma with photosensitivity. Loss-of-function mutations in FERMT1, which located on chromosome 20p12.3, were responsible for KNDLRS. Numerous mutations in FERMT1 have been reported to be associated with KNDLRS.
Results: The present study reported two Chinese KNDLRS families, and affected individuals from both families presented with poikiloderma, palmoplantar hyperkeratosis, and diffuse cigarette paper like atrophy on hands. Skin biopsy of the proband from family 2 showed atrophy of epidermis, hyperkeratosis, dilated blood vessels in upper dermis, and microbubbles at the dermis and epidermis junction. Medical Whole Exome Sequencing V4 combined with Sanger sequencing revealed mutations in FERMT1 with affected individuals. Compound heterozygous nonsense mutations (c.193C>T, c.277C>T) were found with family 1, and a homozygous frameshift mutation (c.220delC) was observed in family 2. According to the clinical features and genetic analysis, KNDLRS was diagnosed in two Chinese families.
Conclusions: This study revealed two novel pathogenic mutations in FERMT1 that caused KNDLRS and briefly summarized all pathogenic mutations in FERMT1 that have been documented via the PubMed.
... Only 23 mutations were revealed to be recurrent in >1 report. Notably, c.676insC was the most common mutation reported in 11 different reports (7,(22)(23)(24)(25)(26)(27)(28)(29)(30)(31) in multiple populations, including German, Albanian, Kosovian, Turkish, Serbian-Greek, Pakistani, Serbian, Australian, Indian, Brazilian and Greek Caucasian, indicating that c.676insC may be a mutation hotspot and serve as a founder effector in the genetic pathogenesis of KS. Furthermore, c.910G>T occurred in 6 reports (20,23,25,27,32,33), c.328C>T in 5 reports (9,20,23,34,35), c.1718+2T>C in 4 reports (20,22,36,37) in multiple different populations and appeared to be relatively common in FERMT1. ...
Kindler syndrome (KS) is a rare subtype of epidermolysis bullosa that is inherited in an autosomal recessive manner with mutations in FERMT1. A number of mutations in FERMT1 have been identified in KS. The current study reported a 33-year-old Chinese man who exhibited a wide variety of clinical features, including formation of blisters, photosensitivity, cutaneous atrophy and poikiloderma, telangiectasia of the face and neck, contracture of the end limbs, nail dystrophy, muscle, eye and oral damage, tympanitis, esophagus narrowing, pneumothorax and palmoplantar keratoderma. The patient's parents were healthy and the patient had no siblings or children. Peripheral blood was obtained from the patient, his parents and 100 controls, who were admitted to the Dermatology Clinic of Shanghai Skin Disease Hospital, Shanghai, China. A multi-gene panel test consisting of 541 genetic loci of monogenic hereditary diseases was performed. The results identified one novel homogenous mutation in the patient: c.1885_1901del (p.Val629fs) on exon 15 in FERMT1. The patient's parents exhibited heterogeneous identical mutations. This mutation was absent in the control group. The results of the multi-gene panel test were further verified by Sanger sequencing. Based on the clinical manifestations and genetic analysis, KS was diagnosed in the patient. The current study reported a Chinese case of KS with one novel mutation c.1885_1901del in FERMT1 and presented a brief summary of all pathogenic mutations in FERMT1 that have been reported in KS between 1984 and May 2020 via a PubMed literature search.
... Revertant mosaicism (Figure 1, Figure S3), with patches of normal skin, can be observed in a few diseases of skin such as ichthyosis with confetti (ichthyosis variegata), epidermolysis bullosa (dystrophic or junctional types, Kindler syndrome and non-Herlitz junctional epidermolysis bullosa. In these, however, the rate of revertant mosaicism is strikingly high 85,[90][91][92][93][94] . The revertant areas may have point mutational mosaicism as demonstrated in epidermolysis bullosa, or disseminated mosaicism as demonstrated in ichthyosis with confetti, or segmental mosaicism as reported in epidermolytic ichthyosis of Brocq 84,86,[95][96][97][98][99][100][101] . ...
Mosaicism denotes an individual who has at least two populations of cells with distinct genotypes that are derived from a single fertilized egg. Genetic variation among the cell lines can involve whole chromosomes, structural or copy-number variants, small or single-nucleotide variants, or epigenetic variants. The mutational events that underlie mosaic variants occur during mitotic cell divisions after fertilization and zygote formation. The initiating mutational event can occur in any types of cell at any time in development, leading to enormous variation in the distribution and phenotypic effect of mosaicism. A number of classification proposals have been put forward to classify genetic mosaicism into categories based on the location, pattern, and mechanisms of the disease. We here propose a new classification of genetic mosaicism that considers the affected tissue, the pattern and distribution of the mosaicism, the pathogenicity of the variant, the direction of the change (benign to pathogenic vs. pathogenic to benign), and the postzygotic mutational mechanism. The accurate and comprehensive categorization and subtyping of mosaicisms is important and has potential clinical utility to define the natural history of these disorders, tailor follow-up frequency and interventions, estimate recurrence risks, and guide therapeutic decisions.
... 88,89 Revertant mosaicism (Fig. 1, Fig. S3), with patches of normal skin, can be observed in a few diseases of skin such as ichthyosis with confetti (ichthyosis variegata), epidermolysis bullosa (dystrophic or junctional types, Kindler syndrome, and non-Herlitz junctional epidermolysis bullosa) In these, however, the rate of revertant mosaicism is strikingly high. 85,[90][91][92][93][94] The revertant areas may have point mutational mosaicism as demonstrated in epidermolysis bullosa, or disseminated mosaicism as demonstrated in ichthyosis with confetti, or segmental mosaicism as reported in epidermolytic ichthyosis of Brocq. 84,86,[95][96][97][98][99][100][101] In ichthyosis with confetti, reversion via loss of heterozygosity (LOH) is a recognized mechanism and, notably, the mitotic recombination events may be multiple and occur independently, each with different inferred start sites for LOH. ...
Mosaicism denotes an individual who has at least two populations of cells with distinct genotypes that are derived from a single fertilized egg. Genetic variation among the cell lines can involve whole chromosomes, structural or copy-number variants, small or single nucleotide variants, or epigenetic variants. The mutational events that underlie mosaic variants occur during mitotic cell divisions after fertilization and zygote formation. The initiating mutational event can occur in any types of cell at any time in development, leading to enormous variation in the distribution and phenotypic effect of mosaicism. A number of classification proposals have been put forward to classify genetic mosaicism into categories based on the location, pattern, and mechanisms of the disease. We here propose a new classification of genetic mosaicism that considers the affected tissue, the pattern and distribution of the mosaicism, the pathogenicity of the variant, the direction of the change (benign to pathogenic vs. pathogenic to benign), and the postzygotic mutational mechanism. The accurate and comprehensive categorization and subtyping of mosaicisms is important and has potential clinical utility to define the natural history of these disorders, tailor follow-up frequency and interventions, estimate recurrence risks, and guide therapeutic decisions.
... The term "natural gene therapy" describes revertant mosaicism, i.e. the spontaneous conversion of a somatic cell with a mutation and pathological phenotype into a cell that has acquired a second, compensating mutation and gained a normal phenotype (18). Revertant mosaicism is relatively common in genetic disorders, and in most classic EB types revertant mosaic skin patches can be found by a well-trained expert. ...
The term skin fragility disorders describes a group of conditions in which the structural integrity of the skin is compromised and its resistance to external shear forces diminished. Skin fragility can have different causes, ranging from genetic variations to inflammatory or physical phenomena. The genetic skin fragility disorders, collectively called epidermolysis bullosa, serve as a paradigm for the study of causes and mechanisms of skin fragility. Recent biomedical research has revealed substantial genetic heterogeneity of the epidermolysis bullosa group, delivered ample new knowledge on its pathophysiology, and facilitated the design of evidence-based therapeutic strategies. The therapy development process extends from in vitro testing to preclinical validation in animal models, and clinical trials. This article reviews different approaches to curative and symptom-relief therapies, and appraises their status and perspectives for clinical implementation.
... Revertant cells proliferate clonally, and mosaic skin patches can be found in all EB types. The genetic mechanisms of the reversion have been characterized, [22] and a successful clinical application of small split thickness grafts derived from revertant skin was reported in an individual with JEB. [23] Cell therapies: have not only led more quickly to clinical studies, but also here the therapeutic context is more complex than initially anticipated. ...
The term epidermolysis bullosa (EB) refers to a group of hereditary skin blistering diseases. The group is clinically and genetically heterogeneous, but all EB forms are associated with mechanically induced skin blistering and fragility. The causative gene mutations of most EB types are known. The current international consensus classification contains four main types: EB simplex (EBS), junctional EB (JEB), dystrophic EB (DEB), and Kindler syndrome (KS). The classification is based on the morphological level of blister formation. In EBS, the split is intra-epidermal, in JEB along the basement membrane and in DEB below the basement membrane. In Kindler syndrome, the dermal-epidermal junction is disorganized, and blisters can occur on all three levels. Each major EB type has further subtypes which may differ in terms of their genetic, biological or clinical characteristics. Traditionally, EB treatments have been symptomatic, but increasing understanding of disease etio-pathogenesis is facilitating development of novel evidence-based therapy approaches. First gene- and cell-based therapies are being tested at preclinical level and in clinical trials. New knowledge on secondary disease mechanisms has led to development and clinical testing of urgently needed symptom-relief therapies using small molecules and biologicals.
... Recent studies have revealed that many adult patients with EB, especially those with JEB, have sporadic areas of normallooking skin on the body where no blister formation is observed even after the skin is rubbed (Almaani et al., 2010; Jonkman et al., 1997;Kiritsi et al., 2012;Lai-Cheong et al., 2011;Pasmooij et al., 2007;Pasmooij et al., 2012). Interestingly, the missing BMZ proteins are restored in these areas, and a portion of the keratinocytes from these sites are recovered from causative gene mutations. ...
Inherited skin disorders have been reported recently to have sporadic normal-looking areas, where a portion of the keratinocytes have recovered from causative gene mutations (revertant mosaicism). We observed a case of recessive dystrophic epidermolysis bullosa treated with cultured epidermal autografts (CEAs), whose CEA-grafted site remained epithelized for 16 years. We proved that the CEA product and the grafted area included cells with revertant mosaicism. Based on these findings, we conducted an investigator-initiated clinical trial of CEAs from clinically revertant skin for recessive dystrophic epidermolysis bullosa. The donor sites were analyzed by genetic analysis, immunofluorescence, electron microscopy, and quantification of the reverted mRNA with deep sequencing. The primary endpoint was the ulcer epithelization rate per patient at 4 weeks after the last CEA application. Three patients with recessive dystrophic epidermolysis bullosa with 8 ulcers were enrolled, and the epithelization rate for each patient at the primary endpoint was 87.7%, 100%, and 57.0%, respectively. The clinical effects were found to persist for at least 76 weeks after CEA transplantation. One of the three patients had apparent revertant mosaicism in the donor skin and in the post-transplanted area. CEAs from clinically normal skin are a potentially well-tolerated treatment for recessive dystrophic epidermolysis bullosa.
