Keratin 17 mutation in pachyonychia congenita type 2 with early onset sebaceous cysts

Coexistence of pachyonychia congenita and hidradenitis suppurativa: more than a coincidence

BACKGROUND

The coexistence of pachyonychia congenita (PC) and hidradenitis suppurativa (HS) has been described in case reports. However, the pathomechanism underlying this association and its true prevalence are unknown.

OBJECTIVES

To determine the genetic defect underlying the coexistence of PC and HS in a large kindred, to delineate a pathophysiological signalling defect jointly leading to both phenotypes, and to estimate the prevalence of HS in PC.

METHODS

We used direct sequencing and a NOTCH luciferase reporter assay to characterize the pathophysiological basis of the familial coexistence of HS and PC. A questionnaire was distributed to patients with PC registered with the International Pachyonychia Congenita Research Registry (IPCRR) to assess the prevalence of HS among patients with PC.

RESULTS

Direct sequencing of DNA samples obtained from family members displaying both PC and HS demonstrated a missense variant (c.275A>G) in KRT17, encoding keratin 17. Abnormal NOTCH signalling has been suggested to contribute to HS pathogenesis. Accordingly, the KRT17 c.275A>G variant resulted in a significant decrease in NOTCH activity. To ascertain the clinical importance of the association of HS with PC, we distributed a questionnaire to all patients with PC registered with the IPCRR. Seventy-two of 278 responders reported HS-associated clinical features (25·9%). Disease-causing mutations in KRT17 were most prevalent among patients with a dual phenotype of PC and HS (43%).

CONCLUSIONS

The coexistence of HS and KRT17-associated PC is more common than previously thought. Impaired NOTCH signalling as a result of KRT17 mutations may predispose patients with PC to HS. What is already known about this topic? The coexistence of pachyonychia congenita (PC) and hidradenitis suppurativa (HS) has been described in case reports. However, the pathomechanism underlying this association and its true prevalence are unknown. What does this study add? A dual phenotype consisting of PC and HS was found to be associated with a pathogenic variant in KRT17. This variant was found to affect NOTCH signalling, which has been previously implicated in HS pathogenesis. HS was found to be associated with PC in a large cohort of patients with PC, especially in patients carrying KRT17 variants, suggesting that KRT17 variants causing PC may also predispose to HS. What is the translational message? These findings suggest that patients with PC have a higher prevalence of HS than previously thought, and hence physicians should have a higher level of suspicion of HS diagnosis in patients with PC.

Identification of clinically useful predictive genetic variants in pachyonychia congenita

BACKGROUND

Pachyonychia congenita (PC) refers to a group of autosomal dominant disorders caused by mutations in five keratin genes (KRT16,KRT6A,KRT17,KRT6B or KRT6C). Current disease classification is based on the gene harbouring disease-causing variants.

AIMS

We harnessed the International Pachyonychia Congenita Research Registry (IPCRR) containing both clinical and molecular data on patients with PC worldwide, to identify genetic variants predicting disease severity.

METHODS

We ascertained 815 individuals harbouring keratin mutations registered in the IPCRR. We looked for statistically significant associations between genetic variants and clinical manifestations in a subgroup of patients carrying mutations found in at least 10% of the cohort. Data were analysed using χ² and Kruskal-Wallis tests.

RESULTS

We identified five mutations occurring in at least 10% of the patients registered in the IPCRR. The KRT16 p.L132P mutation was significantly associated with younger age of onset, presence of palmar keratoderma oral leucokeratosis and a higher number of involved nails. By contrast, the KRT16 p.N125S and p.R127C mutations resulted in a milder phenotype featuring a decreased number of involved nails and older age of onset. Patients carrying the p.N125S mutation were less likely to develop palmar keratoderma while p.R127C was associated with an older age of palmoplantar keratoderma onset. Moreover, the KRT17 p.L99P mutation resulted in an increased number of involved fingernails and patients demonstrating 20-nail dystrophy, while the opposite findings were observed with KRT17 p.N92S mutation.

CONCLUSIONS

We have identified novel and clinically useful genetic predictive variants in the largest cohort of patients with PC described to date.

Steatocystoma multiplex is associated with the R94C mutation in the KRTl7 gene

Steatocystoma multiplex (SM) is an uncommon disorder, characterized by numerous skin-colored subcutaneous cysts. A number of SM pedigrees have been identified with mutations in the keratin 17 (KRT17) gene. The present study examined a four-generation Chinese pedigree with an autosomal dominant mode of inheritance and examined its genetic basis. A review of the literature on KRT17 gene mutations in the SM pedigree was also performed to investigate the KRT17 gene mutation and genotype-phenotype correlation. Exon 1 of the KRTl7 gene was amplified using polymerase chain reaction (PCR) from genomic DNA obtained, which was obtained from 25 family members in the selected Chinese pedigree and from 100 unrelated control individuals. The DNA was then subjected to automatic DNA sequencing. Genealogical investigations demonstrated an autosomal dominant pattern, and direct sequencing of the PCR product revealed a heterozygous mutation, c.280C/T (R94C), which was located in exon 1 of the KRT17 gene in all 10 affected family members. The mutation was not identified in the 15 unaffected family members or in the 100 unrelated control individuals. Therefore, the present study identified a causative mutation in the KRT17 gene in a large Chinese SM pedigree, exhibiting autosomal dominance. A review of the literature suggested that, in addition to the mutation factor, other modifying factors contribute to the phenotype of familial SM.

Pachyonychia congenita type 2, N92S mutation of keratin 17 gene: clinical features, mutation analysis and pathological view

Pachyonychia congenita (PC) type 2 is a rare inherited genetic disease characterized by hypertrophic nail dystrophy, palmoplantar hyperkeratosis and multiple pilosebaceous cysts. In some cases, natal teeth and hair abnormalities may be present. It is caused by mutations in keratin 17 or its expression partner keratin 6b. Here, an N92S (p.Asn92Ser) germline keratin 17 gene mutation in a pachyonychia congenita type 2 female patient is presented. The pedigree includes the 15 members of a family who showed a severe expression of the phenotype for six generations with a similar clinical picture consisting of sebaceous cysts, nail dystrophy, hyperkeratosis, hair abnormalities, natal teeth, hoarseness and hyperhydrosis. In conclusion, we emphasize the importance of diagnosing and managing pachyonychia congenita in childhood for the assistance of affected children and for the development of potential therapies.

Keratin 17 mutation in pachyonychia congenita type 2 patient with early onset steatocystoma multiplex and Hutchinson-like tooth deformity

Pachyonychia congenita type 2 (PC-2) is an autosomal dominant disorder characterized by hypertrophic nail dystrophy, focal keratoderma, multiple pilosebaceous cysts, and other features of ectodermal dysplasia. It has been demonstrated that PC-2 is caused by mutations in the keratin 17 and keratin 6b genes. In this report, we describe a missense mutation in the keratin 17 gene, M88T, in a Korean patient whose phenotype included early onset steatocystoma multiplex and Hutchinson-like tooth deformities along with other typical features of PC-2 such as hypertrophic nails, natal teeth and follicular hyperkeratosis.

Pediatric nail disorders

This article lists common pediatric nail disorders seen in infancy and adolescence. The diagnosis of pediatric nail disorders can be a sign of systemic disorders and diseases. The surgical treatment of young children and the treatment of pediatric patients are presented for those who do not frequently treat pediatric patients. The analysis of pediatric onychomycosis is presented, and the incidence and prevalence in the population is discussed.

A novel mutation of keratin 9 in a large Chinese family with epidermolytic palmoplantar keratoderma

BACKGROUND

Epidermolytic palmoplantar keratoderma (EPPK) is an autosomal dominant inherited skin disorder characterized by diffuse yellow thickening of the skin of the palms and soles, sharply bordered with erythematous margins. Histologically and ultrastructurally, EPPK presents cytolysis of keratinocytes and abnormal aggregation of tonofilaments in the suprabasal layers of the epidermis. To date, 15 different mutations of the keratin 9 gene (KRT9) have been demonstrated to cause most cases of EPPK.

OBJECTIVES

To identify the KRT9 mutation in a large Chinese family with EPPK.

METHODS

Denaturing high-performance liquid chromatography (DHPLC), DNA sequencing and allele-specific polymerase chain reaction (AS-PCR) were used to screen exon 1 of the KRT9 gene for sequence variations.

RESULTS

The DHPLC elution profiles of the DNA fragments amplified from the affected samples differed from those obtained from unaffected individuals, indicating that a sequence variation existed within the analysed fragment of KRT9. DNA sequencing revealed a novel insertion-deletion mutation in the exon 1 of KRT9, 497delAinsGGCT, resulting in the change of tyrosine(166) to tryptophan and leucine (Y166delinsWL). AS-PCR confirmed the mutation was not a common polymorphism.

CONCLUSIONS

The results suggest the molecular basis of EPPK in this Chinese family and provide further evidence that mutations in the helix initiation motif of keratin 9 underlie Chinese EPPK.

Citoqueratinas

As citoqueratinas (CQ) são constituintes do citoesqueleto das células epiteliais, pertencendo aos filamentos intermediários; sua distribuição é específica para cada subtipo de epitélio, permitindo que sejam utilizadas como importantes marcadores de sua diferenciação. Anticorpos monoclonais permitem sua localização nos tecidos e são utilizados no diagnóstico de tumores. Na última década inúmeras mutações foram descritas em seus genes, levando a alteração em sua estrutura molecular, esclarecendo várias enfermidades cutâneas, como epidermólise bolhosa simples (CQ 5 ou 14), hiperqueratose epidermolítica (CQ 1 ou 10), hiperqueratose palmoplantar epidermolítica (CQ 9) e paquioníquia congênita (CQ 6, 16 ou 17).

A Novel Mutation in the Second Half of the Keratin 17 1A Domain in a Large Pedigree with Delayed-Onset Pachyonychia Congenita Type 2

Pachyonychia congenita type 2 (PC-2), also known as Jackson-Lawler type PC, is an autosomal dominant disorder characterized by hypertrophic nail dystrophy associated with focal keratoderma and multiple pilosebaceous cysts. We report a large Chinese pedigree of typical delayed-onset PC-2 that includes 19 affected members. Direct sequencing of PCR products revealed a novel heterozygous 325A-->G mutation in the affected members. This mutation predicts the substitution of asparagine by aspartic acid in codon 109 (N109D) located in the second half of the keratin 17 1A domain, where similar mutation in keratin 5 is associated with the mild Weber-Cockayne form of epidermolysis bullosa simplex.