A glutamine insertion in the 1A alpha helical domain of the keratin 4 gene in a familial case of white sponge nevus

A Rare Clinical Case of Oral White Sponge Nevus and the Associated Challenges in Its Differential Diagnosis

White sponge nevus is a rare genetic autosomal dominant disorder characterized by irregular patches of thick, white diffuse plaques, which mainly affects the oral mucosa and, very rarely, the skin or mucosa of the nose, esophagus, and anogenital region. We present a case of oral white sponge nevus in a 62-year-old woman, the differential diagnosis of which was of particular interest due to other similar white oral lesions, some of which are potentially malignant. The lesions were verified histologically. However, no treatment was performed due to the benign and asymptomatic nature of the lesions.

White Sponge Nevus Caused by Keratin 4 Gene Mutation: A Case Report

White sponge nevus (WSN) is a rare autosomal dominant disease with a family history, often caused by mutations of the keratin 4 (K4) and keratin 13 (K13) genes in patients. It is characterized by frequently occurred white corrugated folds in the bilateral buccal mucosa with soft texture. On histopathological examination, hyperkeratosis of epithelial cells, edema, and vacuolar changes in the spinous cells are observed in the lesions, despite a normal layer of basal cells. WSN should be differentiated from other oral white spot diseases, mainly oral lichen planus, oral candidiasis, oral white edema, and Heck's disease, to reduce misdiagnosis and unnecessary treatment. At present, there is no specific treatment method. The purpose of this study was to report the clinical data of four WSN patients of the same family with the K4 gene mutation. The occurrence of WSN in a pair of monozygotic twins with very similar clinical presentations was identified for the first time. The gene sequencing results showed that there was a heterozygous deletion (C. 438_440delCAA) in exon 1 of the K4 gene, resulting in an aspartic acid loss in both the proband and his father. Finally, the etiology, pathogenesis, pathological manifestations, clinical manifestations, diagnosis, differential diagnosis, and related treatment methods are discussed to provide a reference for clinical treatment of the disease.

Oral White Sponge Nevus: An Exceptional Differential Diagnosis in Childhood

White sponge nevus is an autosomal dominant skin disorder characterized by white, irregular, diffuse plaques mainly affecting the oral mucosa. Histological findings of white sponge nevus are characteristic but not pathognomonic. We report a case of an oral white sponge nevus in a 6-year-old girl, which poses a problem in differential diagnosis with oral candidiasis. No treatment was performed because of the benign and asymptomatic nature of the lesions.

Keratin 4 regulates the development of human white sponge nevus

BACKGROUND

The aim of this study was to investigate the roles of keratin 4 (KRT4) gene in the development of human white sponge nevus (WSN).

METHODS

Transgenic mice were created using the microinjection method with pcDNA3.1 vectors expressing KRT4 wild-type (WT) gene and E520K mutation. Polymerase chain reaction (PCR) and Western blotting were used to identify the genotype of transgenic founders and their filial generations. Expression of KRT4 in mouse oral mucosa was characterized by immunohistochemistry (IHC), and the whole epithelium layer of transgenic mice was observed using transmission electron microscope (TEM).

RESULTS

The positive rate of KRT4 transgenic mice in F1 generation was 45.5%. Expression level of KRT4 protein was significantly higher in 2-month-old transgenic mice than WT mice. Furthermore, all the epithelial lamina of 3-month-old transgenic mice showed reduced staining of KRT4. The surface and spinous layers were full of hyalocytes and bubble cells, which are similar to the clinical symptoms of WSN. For the ultrastructure, both tonofilaments and Odland bodies increased.

CONCLUSIONS

Our study indicated the mutated KRT4 gene may play important roles in the pathogenesis of WSN.

Clinical features and molecular genetic analysis in a Turkish family with oral white sponge nevus

Background

Oral white sponge nevus (WSN) is a rare autosomal dominant benign condition, characterized by asymptomatic spongy white plaques. Mutations in Keratin 4 (KRT4) and 13 (KRT13) have been shown to cause WSN. Familial cases are uncommon due to irregular penetrance. Thus, the aim of the study was: a) to demonstrate the clinical and histopathological features of a three-generation Turkish family with oral WSN b) to determine whether KRT4 or KRT13 gene mutation was the molecular basis of WSN.

Material and Methods

Out of twenty members of the family ten were available for assessment. Venous blood samples from six affected and five unaffected members and 48 healthy controls were obtained for genetic mutational analysis. Polymerase chain reaction was used to amplify all exons within KRT4 and KRT13 genes. These products were sequenced and the data was examined for mutations and polymorphisms.

Results

Varying presentation and severity of clinical features were observed. Analysis of the KRT13 gene revealed the sequence variant Y118D as the disease-causing mutation. One patient revealed several previously unreported polymorphisms including a novel mutation in exon 1 of the KRT13 gene and a heterozygous deletion in exon 1 of KRT4. This deletion in the KRT4 gene was found to be a common polymorphism reflecting a high allele frequency of 31.25% in the Turkish population.

Conclusions

Oral WSN may manifest variable clinical features. The novel mutation found in the KRT13 gene is believed to add evidence for a mutational hotspot in the mucosal keratins. Molecular genetic analysis is required to establish correct diagnosis and appropriate genetic consultation.

Key words:White sponge nevus, leukokeratosis, oral mucosa, keratins, mutation.

Expression profiling of white sponge nevus by RNA sequencing revealed pathological pathways

BACKGROUND

White sponge nevus (WSN) is a rare periodontal hereditary disease. To date, almost all WSN studies have focused on case reports or mutation reports. Thus, the mechanism behind WSN is still unclear. We investigated the pathogenesis of WSN using expression profiling.

METHODS

Sequence analysis of samples from a WSN Chinese family revealed a mutation (332 T > C) in the KRT13 gene that resulted in the amino acid change Leu111Pro. The pathological pathway behind the WSN expression profile was investigated by RNA sequencing (RNA-seq).

RESULTS

Construction of a heatmap revealed 24 activated genes and 57 reduced genes in the WSN patients. The ribosome structure was damaged in the WSN patients. Moreover, the translation rate was limited in the WSN patients, whereas ubiquitin-mediated proteolysis was enhanced.

CONCLUSIONS

Our results suggest that the abnormal degradation of the KRT13 protein in WSN patients may be associated with keratin 7 (KRT7) and an abnormal ubiquitination process.

Current approaches to the diagnosis and treatment of white sponge nevus

White sponge nevus (WSN) in the oral mucosa is a rare autosomal dominant genetic disease. The involved mucosa is white or greyish, thickened, folded and spongy. The genes associated with WSN include mutant cytokeratin keratin 4 (KRT4) and keratin 13 (KRT13). In recent years, new cases of WSN and associated mutations have been reported. Here, we summarise the recent progress in our understanding of WSN, including clinical reports, genetics, animal models, treatment, pathogenic mechanisms and future directions. Gene-based diagnosis and gene therapy for WSN may become available in the near future and could provide a reference and instruction for treating other KRT-associated diseases.

Familial case of oral white sponge nevus--a rare hereditary condition

White sponge nevus (WSN) is an autosomal dominant skin disorder characterized by white, corrugated and diffuse plaques mainly affecting the oral mucosa. The condition has a high penetrance and variable expressivity, but familial reports are uncommon. This report presents a familial case of WSN in which two sisters are affected by the disorder.

White lesions

Increased thickness of the epithelium imparts a white appearance to the oral mucosa by increasing the distance to the underlying blood vessels. Usually this thickening is a result of the increased formation of keratin. Some other less common causes of white lesions are acanthosis or a thickening of the spinous cell layer, edema of the epithelium, or increased fibrosis of the connective tissue thereby reducing blood vessels. Occasionally the surface of an ulcer may appear white, due to collection of fibrin on the surface. In this article the authors discuss white lesions based on putative etiology, that is, hereditary, reactive, inflammation related, immunologic, traumatic, infection related, and idiopathic.

Evaluation of oral mucosal lesions in 598 referred Iranian patients

The mucosal membrane of the oral cavity displays at times classical developmental lesions considered to be variations of normal structures rather than having disease characteristics. Of these lesions leukoedema, Fordyce granules, geographic-, fissured- and hairy tongue, median rhomboid glossitis and lingual varices were studied in 598 patients referred to the School of Dentistry, Tehran, Iran. The prevalence was studied in relation to age, gender, occupation, education, smoking habits, general health, addictions and or drug therapies. Oral developmental lesions were seen in 295 patients (49.3%). Only Fordyce granules (27,9%), fissured tongue (12,9%), leukoedema (12,5%) and hairy tongue (8,9%) had enough cases for statistical analysis. Three of these lesions increased with age but not fissured tongue. All were more common in men. After adjusting for age, the parameters education, occupation and complaints upon referral had little influence on the prevalence of the lesions. Fewer Fordyce granules were seen in oral mucosa of smoking men. Leukoedema and hairy tongue were significantly associated with smoking, leukoedema with diabetes mellitus. We conclude that there was a highly significant association between these oral lesions and age, gender and smoking. Few significant associations were found between oral lesions and general diseases.

Two new mutations in the keratin 4 gene causing oral white sponge nevus in Chinese family

OBJECTIVE

We investigated white sponge nevus (WSN) in a Chinese family, and tried to find new mutation and demonstrated that this mutation is the causative mutation for WSN in this family and this condition affects a functionally important segment of the keratin 4 protein.

MATERIALS AND METHODS

We studied the affected family with the 32-year-old female patient, her mother, her younger sister and her daughter. Pathologic examinations were performed. DNA was extracted from peripheral blood lymphocytes, K4 and K13 genes were amplified by polymerase chain reaction (PCR) and sequenced.

RESULTS

Direct sequencing of PCR products revealed two new mutations in the keratin 4 gene, the heterozygous missense mutation 1829G-->A in exon 2B, and 2324A-->G in non-coding region. No any mutation was found in the keratin 13 gene.

CONCLUSIONS

We found two new mutations in the keratin 4, which may be related with the development of WSN.

White sponge nevus: report of a three-generation family

OBJECTIVE

White sponge nevus (WSN) is a rare autosomal dominant disorder that results in soft, white, and spongy plaques in the oral mucosa. The aim of this study was to describe the clinical, histopathologic, and genetic features of a family, spanning 3 generations, affected by WSN.

STUDY DESIGN

This study was performed using a cross-sectional layout analyzing a family with WSN.

RESULTS

Clinical examination of family members revealed that of 23 descendants, 8 (34.78%) had WSN features. Unaffected and affected members transmitted the disease to their offspring. The offspring recurrence risk was 0.34, and an incomplete level of penetrance was observed. The lesions showed many clinical and histopathologic similarities to cases previously reported. The most affected sites were buccal and labial mucosa, with a rare appearance in the palate. No extraoral lesion was found. Histological examination showed intense acanthosis and hyperparakeratosis-induced epithelial hyperplasia. Within the spinous layer, cells showing perinuclear eosinophilic condensation of the cytokeratin (CK) filaments were frequent.

CONCLUSION

The disease was transmitted by an autosomal dominant mode of inheritance, appearing mainly in the buccal and labial mucosa.

Identification of a Keratin 4 Mutation in a Chemically Induced Mouse Mutant that Models White Sponge Nevus

With the goal of increasing the number of genetic entry points for studying physiologic processes and human disease, large-scale, systematic, chemical mutagenesis projects in mice have been initiated in several different centers. We have been studying mouse mutants that exhibit dominantly inherited defects in either skin and/or hair color. Here, we describe a bright coat color mutant, Bright coat color 1 (Bcc1), which develops light-colored hair at 4 weeks of age, and when homozygous exhibits oral leukoplakia and blistering, and growth retardation. We identified a missense mutation in mutant animals that predicts an N154S amino-acid substitution in the 1A domain of Keratin 4 (encoded by the Krt2-4 gene), a region known to be mutated in human patients with white sponge nevus (WSN). Bcc1 recapitulates the gross pathologic, histologic, and genetic aspects of the human disorder, WSN.

A novel arginine substitution mutation in 1A domain and a novel 27 bp insertion mutation in 2B domain of keratin 12 gene associated with Meesmann's corneal dystrophy

AIM

To determine the disease causing gene defects in two patients with Meesmann's corneal dystrophy.

METHODS

Mutational analysis of domains 1A and 2B of the keratin 3 (K3) and keratin 12 (K12) genes from two patients with Meesmann's corneal dystrophy was performed by polymerase chain reaction amplification and direct sequencing.

RESULTS

Novel mutations of the K12 gene were identified in both patients. In one patient a heterozygous point mutation (429A-->C = Arg135Ser) was found in the 1A domain of the K12 gene. This mutation was confirmed by restriction digestion. In the second patient a heterozygous 27 bp duplication was found inserted in the 2B domain at nucleotide position 1222 (1222ins27) of the K12 gene. This mutation was confirmed by gel electrophoresis. The mutations were not present in unaffected controls.

CONCLUSION

Novel K12 mutations were linked to Meesmann's corneal dystrophy in two different patients. A missense mutation replacing a highly conserved arginine residue in the beginning of the helix initiation motif was found in one patient, and an insertion mutation, consisting of a duplication of 27 nucleotides, was found before the helix termination motif in the other.

Constitutional mutation of keratin 13 gene in familial white sponge nevus

OBJECTIVE

We sought to investigate a novel mutation in the keratin genes assumed to be responsible for a familial case of oral white sponge nevus.

PATIENTS AND METHODS

The affected family consisted of a 36-year-old woman, her 17-year-old daughter, and her 14-year-old son. Keratin 4 and 13 genes extracted from venous blood lymphocytes were amplified by using the polymerase chain reaction and directly sequenced.

RESULTS

Sequencing analysis of the 3 patients revealed the presence of a novel heterozygous T-to-C transition mutation in exon 1 of the keratin 13 gene, with no abnormalities detected in the keratin 4 gene.

CONCLUSION

We identified a novel heterozygous missense mutation at 332T>C in the keratin 13 gene believed to be related to the development of white sponge nevus.

The molecular genetics of keratin disorders

Keratins are the type I and II intermediate filament proteins which form a cytoskeletal network within all epithelial cells. They are expressed in pairs in a tissue- and differentiation-specific fashion. Epidermolysis bullosa simplex (EBS) was the first human disorder to be associated with keratin mutations. The abnormal keratin filament aggregates observed in basal cell keratinocytes of some EBS patients are composed of keratins K5 and K14. Dominant mutations in the genes encoding these proteins were shown to disrupt the keratin filament cytoskeleton resulting in cells that are less resilient and blister with mild physical trauma. Identification of mutations in other keratin genes soon followed with attention focussed on disorders showing abnormal clumping of keratin filaments in specific cells. For example, in bullous congenital ichthyosiform erythroderma, clumping of filaments in the suprabasal cells led to the identification of mutations in the suprabasal keratins, K1 and K10. Mutations have now been identified in 18 keratins, all of which produce a fragile cell phenotype. These include ichthyosis bullosa of Siemens (K2e), epidermolytic palmoplantar keratoderma (K1, K9), pachyonychia congenita (K6a, K6b, K16, K17), white sponge nevus (K4, K13), Meesmann's corneal dystrophy (K3, K12), cryptogenic cirrhosis (K8, K18) and monilethrix (hHb6, hHb1).In general, these disorders are inherited as autosomal dominant traits and the mutations act in a dominant-negative manner. Therefore, treatment in the form of gene therapy is difficult, as the mutant gene needs to be inactivated. Ways of achieving this are actively being studied. Reliable mutation detection methods from genomic DNA are now available. This enables rapid screening of patients for keratin mutations. For some of the more severe phenotypes, prenatal diagnosis may be requested and this can now be performed from chorionic villus samples at an early stage of the pregnancy. This review article describes the discovery of, to date, mutations in 18 keratin genes associated with inherited human diseases.

A novel mutation in the keratin 4 gene causing white sponge naevus

BACKGROUND

White sponge naevus (WSN) is a rare, autosomal dominant disorder that predominantly affects noncornified stratified squamous epithelia, most commonly the buccal mucosa. Clinically, WSN manifests as thickened spongy mucosa with a white opalescent tint in the mouth and may be confused with other disorders that cause white lesions on oral mucosa. Recent studies have identified pathogenic mutations in KRT4 and KRT13, the genes encoding mucosa-specific keratins, in WSN.

OBJECTIVES

To search for possible mutations in KRT4 and KRT13.

METHODS

We report a case of WSN in a young man who presented with diffuse irregular whitish plaques involving the buccal and gingival mucosae and the tongue. Results Pathologically, the affected mucosa showed epithelial thickening, parakeratosis and extensive vacuolization of the suprabasal keratinocytes. Mutation analysis revealed a heterozygous missense mutation 1345G-->A in KRT4, predicting an amino acid change, E449K, in the 2B domain of the K4 polypeptide.

CONCLUSIONS

We report the first mutation analysis of a Taiwanese patient with WSN. Potentially this novel mutation could disrupt the stability of keratin filaments and result in WSN.

A novel mutation in the keratin 13 gene causing oral white sponge nevus

White sponge nevus (WSN) is an autosomal-dominantly inherited form of mucosal leukokeratosis. Defects in keratins, proteins that form the stress-bearing cytoskeleton in epithelia, have been shown to cause several epithelial fragility disorders. Recently, mutations in the genes encoding mucosal-specific keratins K4 and K13 were shown to be the underlying cause of WSN. We have studied a large Scottish family with 19 persons affected by WSN in four generations. The K4 locus was excluded by genetic linkage analysis; however, genetic linkage consistent with a K13 defect was obtained. Subsequently, a heterozygous missense mutation 335A>G was detected in exon 1 of the KRT13 gene, predicting the amino acid change N112S in the 1A domain of the K13 polypeptide. The mutation was confirmed in affected family members and was excluded from 50 unaffected people by restriction enzyme analysis. These results confirm that mucosal keratin defects are the cause of WSN.