Coexistence of KRT 14 and KRT 5 mutations in a P olish patient with epidermolysis bullosa simplex

DEAR EDITOR, Epidermolysis bullosa simplex (EBS) is a rare hereditary genodermatosis characterized by intraepidermal skin blistering upon mild trauma. The most frequent subtypes are EBS-generalized non-Dowling–Meara (EBS-gen nDM) and EBSlocalized (EBS-loc). Approximately 75% of EBS cases are caused by mutations in the KRT5 and KRT14 genes encoding keratin 5 (K5) and keratin 14 (K14), respectively. Dominantly acting missense mutations occur in most cases. K14 and K5 form obligatory heterodimers, which selfassemble into intermediate filaments, the most important cytoskeleton element conferring epidermal resistance to mechanical stress. Each keratin molecule is composed of a head (N-terminal end), tail (C-terminal end) and a central L-helical rod domain, which is divided into helical segments responsible for dimerization (1A, 1B, 2A and 2B) separated by nonhelical linkers. EBS can be inherited in autosomal dominant or recessive mode. The severity of the disease depends on the domain affected, amino acid position within the heptad structure, (abcdefg)n of the helical domain and alterations in biophysical properties. We present an EBS family with three different phenotypes caused by a mutation in either KRT5 or KRT14, or digenic mutations in the KRT5 and KRT14 genes (Fig. 1). The proband was a 3-year-old boy with generalized blistering at birth, born to nonconsanguineous parents. Blisters, also localized in oral and anal mucous membranes, tended to heal without scars; the toenails had peeled off a number of times. The skin lesions diminished with time and, at the age of 3 years, were localized to the feet, hands and knees and appeared after mechanical stress. At this time, a clinical diagnosis of EBS-gen nDM (formerly EBS-Koebner) was considered. The proband’s father was diagnosed with EBS-loc and had spontaneous and stress-induced blisters restricted to the soles from birth; no mucous membranes were involved. Several other members of his family were similarly affected with EBS-loc. However, according to the proband’s father, boys in the family were more prone to lesion development than girls, who in turn experienced occasional blistering induced by underwear and sanitary pads. The proband’s mother revealed that she suffered from skin fragility on the feet, where blisters occurred after mild trauma; together with her mother (the proband’s grandmother), she asked for a dermatologist consultation because of cracking feet. Mutational analysis of KRT5 (reference sequence: NM_000424) and KRT14 (NM_000526) in the proband was performed using Sanger sequencing of all coding regions (primers published previously or designed in Primer3). The control group consisted of 100 DNA samples isolated from healthy people and was analysed by restriction fragment length polymorphism (using SsiI and Alw26I restriction enzymes). We identified two mutations in the proband: p.Arg471His (c.1412G>A) in KRT5 and p.Met272Thr (c.815T>C) in KRT14. The p.Met272Thr is a mutation that has been reported several times in patients with EBS of different subtypes: EBS-DM,