BACKGROUND: Epidermolysis bullosa simplex (EBS) is a mechanobullous 
genodermatosis that may be caused by mutations in the genes KRT5 and KRT14 
encoding the basal epidermal keratins 5 (K5) and 14 (K14). Three main clinical 
subtypes of EBS exist, differing in onset, distribution and severity of skin 
blistering. Previous reports of KRT5 and KRT14 mutations suggest a correlation 
between the location of the mutation and the severity of the associated EBS 
phenotype.
OBJECTIVES: The prevalence of KRT5/KRT14 mutations and the genotype-phenotype 
correlation in the largest tissue-confirmed EBS population is investigated.
METHODS: KRT5 and KRT14 genomic DNA and cDNA sequences of 76 clinically 
well-defined unrelated EBS probands were amplified and then subjected to direct 
sequencing and product length analysis. Immunofluorescence microscopy on 
patients' skin biopsies with antibodies against K5 and K14 was performed to 
study protein expression.
RESULTS: In 57 of 76 (75%) probands 41 different KRT5 and KRT14 mutations were 
identified, of which 12 were novel. Mutations affecting the highly conserved 
helix boundary motifs of the rod domains of K5 and K14, and the K14 helix 
initiation motif in particular, were associated with the severest, EBS 
Dowling-Meara, phenotype. In 21 EBS probands (37%) the mutation was de novo. In 
19 probands (25%) KRT5 or KRT14 mutations were excluded.
CONCLUSIONS: The phenotype-genotype correlation observed in this large EBS 
population underscores the importance of helix boundary motifs for keratin 
assembly. Only three-quarters of biopsy-confirmed EBS probands have KRT5 or 
KRT14 mutations, indicating genetic heterogeneity in EBS. Alternative gene 
candidates are discussed.