Acta Dermato-Venereologica, issue 9 97-9CompleteContent | Page 16

1114 CLINICAL REPORT A Review of 52 Pedigrees with Epidermolysis Bullosa Simplex Identifying Ten Novel Mutations in KRT5 and KRT14 in Australia Emma N. KIM 1,2 , Adam G. HARRIS 1,2 , Linda J. BINGHAM 3,4 , Wenfei YAN 2 , John C. SU 3,4 and Dedee F. MURRELL 1,2 Department of Dermatology, St George Hospital, 2 Faculty of Medicine, University of New South Wales, Sydney, 3 Department of Paediatrics, Murdoch Children’s Research Institute/University of Melbourne, Royal Children’s Hospital, Parkville, and 4 Faculty of Medicine, Monash University, Eastern Health, Box Hill, Australia 1 Epidermolysis bullosa simplex (EBS) is a rare herita- ble skin fragility disorder, most commonly caused by dominant mutations in KRT5 and KRT14. EBS shows clinical heterogeneity with localised, intermediate and generalised severe forms, which tend to correlate with the location and nature of the disease causing muta- tions. We therefore aimed to identify the KRT5 and KRT14 mutations in patients diagnosed with EBS in Australia, and explore in depth the genotype to the phenotype correlations in patients with novel variants. Australian patients who were diagnosed with EBS af- ter referral to the Australian National Diagnostic Labo- ratory for EB were offered mutation screening in the KRT5 and KRT14 genes. From this, 32 different mu- tations in KRT5 and KRT14 were identified within 39 of 52 pedigrees. Ten of these mutations from 9 diffe- rent pedigrees were novel, a further fatal case caused by KRT5 E477K is reported and in addition the third reported case of digenic inheritance in EBS was also observed. Key words: epidermolysis bullosa simplex; keratin 5; keratin 14. Accepted May 30, 2017; Epub ahead of print May 31, 2017 Acta Derm Venereol 2017; 97: 1114–1119. Corr: Pro fessor Dedee F. Murrell, Department of Dermatology, Ground floor James Law House, St George Hospital, Gray Street, Sydney, New South Wales, Australia. E-mail: [email protected] in a form that is milder than EBS-gen severe. EBS-gen severe, resembling the eponymous EBS-Dowling Meara, involves widespread clustered blistering, erosions, scar- ring, milia and can involve the mucous membranes, hair and the nails (4). The different EB subtypes tend to correlate with the location and nature of the inherited mutation (5). The highly conserved ends of the rod domain (helix boundary motifs) of KRT5 and KRT14 are crucial for correct keratin filament assembly and mutations in these regions often result in severe blistering, whereas mutations outside of these regions tend to cause milder phenotypes of EBS (6). Despite this knowledge, genotype–phenotype pre- dictions must be performed with caution, as the process of gene expression is complex and can be influenced by other genetic and epigenetic factors (7). It is therefore essential that genotype–phenotype correlations are pu- blished, especially those of patients with novel mutations and unexpected phenotypes, as this can lead to a better understanding of the pathogenesis of EBS, clarify prog- nosis and assist in prenatal testing (8). We aim to review the KRT5 and KRT14 mutations known to cause EBS in the Australian population and look in depth at the pedigrees in which we found novel mutations. METHODS E pidermolysis bullosa simplex (EBS) is a heritable di- sease most commonly caused by dominant-negative mutations in the genes encoding keratin 5 and keratin 14 (KRT5 and KRT14) (1). Keratin 5 and 14 dimerise to form intermediate filaments, which provide structure, strength and flexibility to the keratinocyte cytoskeleton. When compromised, they are susceptible to mechanical stress, leading to the fracture of basal keratinocytes and subsequent blistering of the epithelium (2). EBS exhibits clinical heterogeneity with 3 main subtypes (3). Epidermolysis bullosa simplex-localised (EBS-loc), resembling the previously used eponymous EBS-Weber Cockayne, is the most common form and is characterised by blistering confined to soles and palms, worse with friction, trauma, heat and sweating (3). EBS-gen intermediate, resembling the eponymous EBS- Koebner, presents with more widespread blistering, but doi: 10.2340/00015555-2715 Acta Derm Venereol 2017; 97: 1114–1119 Patients We performed a cross-sectional analysis using patient data from both the Australian National Diagnostic Laboratory Database for EB (9) and the Australasian EB Registry (10). Patients included in the study were located in Australia and had a confirmed diagnosis of EBS based on a combination of clinical history, immunofluo- rescence mapping (IFM) and electron microscopy (EM). Data gathered included sequencing results of both KRT5 and KRT14 and clinical phenotypes. If phenotypic data was unclear, patient records were reviewed and the patient was contacted and reviewed in person if further information was needed. Mutation analysis Mutation screening was performed on blood samples obtained with informed consent. Genomic DNA was extracted using a commer- cial kit (Qiagen Blood DNA Kit; Qiagen, Hilden, Germany) and analysed by bi-directional sequencing of exons 1–9 of KRT5 and exons 1–8 of KRT14. The study was approved by the South Eastern Sydney Local Health District Human Research Ethics Committee. This is an open access article under the CC BY-NC license. www.medicaljournals.se/acta Journal Compilation © 2017 Acta Dermato-Venereologica.