Intractable & Rare Diseases Research | A Novel KRT5 Gene c.987C>G Mutation Causes Epidermolysis Bullosa Simplex

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This study identified a novel KRT5 gene mutation and validated its pathogenicity through familial co-segregation analysis. The mutation leads to a mild clinical phenotype and provides new reference for molecular diagnosis and genetic counseling of EBS.

 

Literature Overview
This article, 'Clinical and genetic study of a family with epidermolysis bullosa simplex caused by a novel KRT5 gene mutation c.987C>G (p.Asn329Lys)', published in the journal Intractable & Rare Diseases Research, reviews and summarizes the clinical and genetic features of an EBS family carrying a novel KRT5 mutation. It further analyzes the pathogenicity of this mutation and its correlation with clinical phenotypes, providing important evidence for molecular diagnosis and genetic counseling of EBS.

Background
Epidermolysis bullosa simplex (EBS), the most common subtype of epidermolysis bullosa, is mainly caused by mutations in the KRT5 or KRT14 genes, which encode keratin 5 and keratin 14. These proteins form a heterodimeric complex and assemble into the intermediate filament network, maintaining mechanical stability in basal epidermal cells. Most KRT5 mutations are dominant-negative missense mutations, and the mutation position is closely correlated with the severity of the clinical phenotype. Current studies on EBS primarily focus on mutation localization and their impact on keratin structure and function, but the genotype-phenotype relationship remains unclear and the pathogenic mechanisms are complex. This study identifies a novel mutation through whole-exome sequencing combined with bioinformatics analysis, and further supports its pathogenicity through familial co-segregation and conservation analysis, offering a new perspective for EBS clinical diagnosis and genetic counseling.

 

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Study Methods and Experiments
The study enrolled a 20-year-old female proband and a total of 8 family members (5 affected individuals and 2 unaffected individuals). Genomic DNA was extracted from peripheral blood samples and whole-exome sequencing was performed. Sanger sequencing was used to validate candidate mutations. Functional prediction was conducted using SIFT, PolyPhen-2, and MutationTaster. Conservation analysis was carried out using ConSurf and the NCBI CDD database, and the pathogenicity of the mutation was assessed according to the 2015 ACMG guidelines.

Key Findings and Perspectives

• All affected individuals in the proband's family, including the proband, carry the heterozygous KRT5 c.987C>G (p.Asn329Lys) mutation, while unaffected individuals do not, consistent with an autosomal dominant inheritance pattern.
• This mutation is not recorded in databases such as gnomAD and represents the first international report of this novel variant.
• Bioinformatics analysis showed a SIFT score of 0.00 (damaging), PolyPhen-2 score of 1.000 (probably damaging), and MutationTaster prediction of 'damaging'.
• ConSurf analysis indicated that the amino acid at position 329 is highly conserved (score 0.92), and NCBI CDD database confirmed its location within the Filament domain of the KRT5 protein (E-value = 1.04e–158).
• According to ACMG pathogenicity criteria, this mutation is classified as 'pathogenic'.
• The clinical phenotype is mild EBS, characterized by friction-induced blisters, seasonal dependency, and scar-free healing.

Significance and Future Directions
This study identifies a novel pathogenic KRT5 mutation, providing a new target for molecular diagnosis of EBS. Its unique phenotypic features expand the genotype-phenotype spectrum of EBS, improving diagnostic efficiency and accuracy of genetic counseling. Future studies may involve constructing expression vectors with this mutation to observe its interaction with KRT14 and its impact on intermediate filament assembly, directly validating the pathogenic mechanism. Moreover, the mutation lies within the highly conserved Filament domain, offering a potential intervention target for gene therapy strategies.

 

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Conclusion
This study reports the pathogenicity of the KRT5 c.987C>G (p.Asn329Lys) mutation in an EBS family through whole-exome sequencing, Sanger sequencing validation, bioinformatics prediction, and familial co-segregation analysis, confirming it as a de novo pathogenic variant. The clinical phenotype includes friction-induced blisters, seasonal dependency, and scar-free healing, representing a mild form of EBS. The mutation resides in the Filament domain of KRT5, which is highly conserved. Multiple prediction tools consistently indicate a damaging effect. These findings provide new references for molecular diagnosis, genetic counseling, and prenatal testing of EBS, and offer a potential therapeutic target for future gene therapy. Although in vitro functional studies are lacking, this study significantly expands the spectrum of pathogenic variants associated with EBS and provides a useful molecular marker for clinical diagnosis.

 

Ruohan Zhang, Xu Chen, Zhenying Wang, Chao Xu, and Shenhao Li. Clinical and genetic study of a family with epidermolysis bullosa simplex caused by a novel KRT5 gene mutation c.987C>G (p.Asn329Lys). Intractable & Rare Diseases Research.