A novel missense mutation L468Q of keratin 6a in pachyonychia congenita type 1

A novel heterozygous frameshift mutation in the KRT6A gene responsible for an uncommon phenotype of pachyonychia congenita: One case report and review of literature

Pachyonychia congenita is an uncommon autosomal dominant skin disorder characterized by hypertrophic nail dystrophy, palmoplantar keratoderma, oral leukokeratosis, and cutaneous cysts. And fissured tongue is rarely reported in patients with pachyonychia congenita. The disease is primarily associated with mutations in five keratin genes, namely KRT6A, KRT6B, KRT6C, KRT16 or KRT17. Herein we report a 9-year-old Chinese girl who has thickened nails, keratinized plaques, and fissured tongue since birth. To investigate the underlying genetic cause, whole-exome sequencing and Sanger sequencing were performed in this patient and her family members. We identified a candidate variant c.1460-2_1460del (p.S487Lfs*21) in the KRT6A gene (NM_005554.4) by whole-exome sequencing. Sanger sequencing revealed the absence of the mutation in both parents, indicating that it is a de novo variant. Thus, the novel heterozygous frameshift mutation c.1460-2_1460del (p.S487Lfs*21) within exon 9 of KRT6A was identified as the genetic cause of the patient. Our study identified a rare de novo heterozygous frameshift mutation in the KRT6A gene in a patient with pachyonychia congenita presenting fissured tongue. Our findings expand the KRT6A gene mutation spectrum of Pachyonychia congenita, and will contribute to the future genetic counseling and gene therapy for this disease.

Distinctions in the Management, Patient Impact, and Clinical Profiles of Pachyonychia Congenita Subtypes

Introduction

Pachyonychia congenita (PC) is a rare dermatosis that confers lifelong physical and emotional morbidities in affected patients. However, the clinical findings, treatments, and psychosocial impact of this disease have not been adequately described. The International PC Research Registry (IPCRR), a multinational initiative to collect data on PC patients, has allowed an opportunity to distinguish the salient features of this disease. We aimed to characterize the breadth and extent of nail disease, treatments, and quality of life in PC patients, and to describe any significant differences in clinical presentation or treatment of PC subtypes.

Methods

The most recent IPCRR patient survey data consisting of an 857-response questionnaire and a 102-response addendum were analyzed in a retrospective analysis. The survey data were collected as part of a multinational, multicenter initiative and comprise the largest representative population of PC to date. Participants (survey respondents) were included in the study based on questionnaire responses and a genetic confirmation of having a PC subtype.

Results

A total of 857 survey responses were collected. Genetic variations among PC subtypes influence nail disease onset and severity of symptoms. Nail disease negatively impacts patients' emotional health, especially during the adolescent and young adult years. Nail treatment tools vary little in terms of effectiveness and acquired infection rates.

Conclusion and Discussion

Patients with different PC subtypes have distinct clinical nail presentations and psychosocial impact. Genetic testing should be used to confirm PC diagnoses. Further characterization of PC, especially the rarer subtypes, may allow for more individualized patient education.

Generalized bullae in a young girl with KRT6A-related pachyonychia congenita

Pachyonychia congenita (PC) is a rare genodermatosis showing heterogeneity with five causative keratin genes (KRT6A, KRT6B, KRT6C, KRT16, or KRT17). Clinically, PC is characterized by hypertrophic onychodystrophy, painful palmoplantar keratoderma, oral leukokeratosis, and follicular hyperkeratosis. We describe an atypical case of PC in a young Chinese girl presenting with generalized bullae and identified a recurrent heterozygous missense mutation c.1406T > C (p.Leu469Pro) in KRT6A. This suggests that bullae may represent an important feature of KRT6A-related PC.

A spectrum of mutations in keratins K6a, K16 and K17 causing pachyonychia congenita

BACKGROUND

Pachyonychia congenita (PC) is a rare autosomal dominant keratin disorder, subdivided into two major variants, PC-1 and PC-2. Predominant characteristics include hypertrophic nail dystrophy, focal palmoplantar keratoderma and oral leukokeratosis. Multiple steatocystomas that develop during puberty are a useful feature distinguishing PC-2 from PC-1. At the molecular level it has been shown that mutations in keratin K6a or K16 cause PC-1 whereas those in K6b or K17 lead to PC-2.

OBJECTIVE

To identify mutations in 22 families presenting with clinical symptoms of either PC-1/focal non-epidermolytic palmoplantar keratoderma (FNEPPK) or PC-2.

METHODS

Mutation analysis was performed on genomic DNA from PC patients by direct sequencing.

RESULTS

Here, we report four new missense and five known mutations in K6a; one new deletion and three previously identified missense mutations in K16; plus one known mutation in K17.

CONCLUSION

With one exception, all these heterozygous mutations are within the highly conserved helix boundary motif regions at either end of the keratin rod domain. In one sporadic case, a unique mutation in K16 resulting in deletion of 24bp was found within the central rod domain, in a child with a phenotype predominantly consisting of focal plantar keratoderma. The identification of mutations in cases of PC is prerequisite for future development of gene-specific and/or mutation-specific therapies.