Department of Dermatology, University of Freiburg, Freiburg, Germany

Correspondence: Cristina Has, MD, Department of Dermatology, University of Freiburg, Hauptstr. 7, 79104 Freiburg, Germany. Email: crishas@haut.ukl.uni-freiburg.de

Received 11 August 2003; Revised 29 September 2003; Accepted 1 October 2003.

To the Editor:

Here we report a novel homozygous nonsense mutation in the KIND1 (kindlerin) gene in a patient previously thought to have epidermolysis bullosa simplex with mottled pigmentation (EBS-MP).

Kindler syndrome (KS) (MIM 173650) is a rare autosomal recessive genodermatosis. The main characteristics are congenital skin blistering that resolves slowly with age, mild photosensitivity that improves with age, and early, generalized, progressive poikiloderma with extensive atrophy (^{Patrizi et al, 1996}). The presence of palmoplantar keratoderma and nail abnormalities is variable; webbing of the fingers and contractures may occur. Gingival fragility, poor dentition, as well as early and rapidly progressive periodontitis are common features (^{Wiebe et al, 2003}). Other mucous membranes, i.e., urethral, anal, oesophageal, and genital (^{Binder et al, 2002}) mucosae, may be involved. The lesions can lead to stenosis of the respective organs. Squamous cell carcinoma of the hard palate (^{Lotem et al, 2001}), the lip, and a transitional cell carcinoma of the urinary bladder have been reported as complications of KS (^{Alper et al, 1978}).

Very recently, the gene responsible for KS was localized on the short arm of chromosome 20, and mutations in a new gene, designated as kindlerin, were identified in four families (^{Jobard et al, 2003}).^{Siegel et al (2003)} could demonstrate homozygous nonsense and frameshift mutations in the same gene (which they called KIND1) in 17 families with KS. The protein, kindlin-1, is a component of focal contacts, structures involved in membrane-substratum attachment in cultured cells.

The index patient is a 35-y-old Caucasian man who had a history of acral blistering since birth. The family history was negative for skin diseases, and consanguinity was not known. The blisters and erosions healed sometimes with atrophy and milia, but generally without scars. Mild photosensitivity was noted. Gingival fragility was present and periodontitis was diagnosed since childhood. At the age of 18, physical examination revealed slight atrophy of the integument with mottled hyperpigmentation and hypopigmentation on the trunk Figure 1a, axillae Figure 1b, face, and extremities. On the dorsal aspects of the hands and the knees "cigarette-paper-like" atrophy was present Figure 1c. Mild diffuse palmoplantar keratosis, slight contractures and webbing of the fingers Figure 1d, and dystrophy of some toenails were observed. Mucosal involvement consisted of gingival bleeding and perianal erosions. Based on the clinical findings at that time, the diagnosis of EBS-MP was established (^{Bruckner-Tuderman et al, 1989}). Our investigation has been approved by the Institutional Review Board and was conducted according to the declaration of the Helsinki Principles. Blood samples from the patient and his parents were collected after signing the consent forms.

Figure 1.

Clinical features of the index patient. (a) Extensive atrophy on the trunk; (b) mottled hyperpigmentation in the right axilla; (c) cigarette-paper-like atrophy on the dorsal aspects of the hands; (d) mild palmoplantar keratoderma.

Full figure and legend (124K)

At the age of 35, the status of the integument was stable and the symptoms generally mild. Photosensitivity was moderate and could be managed well with continued use of sunscreens. Mechanically induced acral blistering was present; mostly the feet were affected, and some erosion healed slowly. Palmoplantar keratoses and interdigital webbing had led to finger contractures, and painful fissures formed over ventral small joints. Toenails had become increasingly dystrophic, and the great toenails were permanently lost. Fragility of the oral mucosa continued, but periodontitis had improved with age. Frequent corneal erosions caused pain and discomfort but did not affect visual acuity. Perianal erosions caused light bleeding.

Immunofluorescence staining of the dermal-epidermal junction with antibodies to basement membrane proteins demonstrated that BP230, laminin 5, collagen IV, and collagen VII were localized to the blister floor and had an irregular, broad, and interrupted segmental pattern. Electron microscopy disclosed a split at the subnuclear level inside the basal keratinocytes. The basement membrane was focally ramified and interrupted at several points, and some basal keratinocytes showed intracellular vacuolization, disappearance of the cellular organelles, and sparse, clumped tonofilaments.

The analysis of the coding sequence and exon-intron boundaries of the KIND1 gene (performed as described by^{Jobard et al, 2003}) disclosed a homozygous sequence variant G-to-T at position 910 in exon 7. Consequently, the codon 304 GAA for glutamic acid was changed to TAA, a stop codon Figure 2a, and the mutation was designated as E304X. Both parents were heterozygous for this mutation. The mutation was verified by restriction enzyme digestion with Mbo II Figure 2b. Sequencing of the KRT5 gene had been performed previously. The P25L missense mutation, which has been identified in most patients with EBS-MP, was not detected in our patient.

Figure 2.

Mutation analysis. (a) Normal sequence in control individual (upper panel), homozygous sequence 910G > T in the patient (middle), and heterozygous status of a parent (lower panel). (b) Pedigree and restriction enzyme digestion analysis with Mbo II. UD, undigested product of 432 bp; NC, normal control with 170 bp and 127 bp bands; F, father with 191 bp, 170 bp, and 127 bp bands; M, mother with 191 bp, 170 bp, and 127 bp bands; p, proband with 191 bp and 127 bp bands. The 191 bp and 170 bp bands are indicated by red arrows.

Full figure and legend (53K)

The novel nonsense mutation E304X in the KIND1 gene is predicted to cause loss of the FERM (filopodin and ezrin/radixin/moesin) and PH (pleckstrin homology) domains and consequently to impair the function of the protein or, more likely, to lead to nonsense-mediated mRNA decay and complete loss of kindlin-1 protein expression. The long follow-up period of the patient allowed us to observe the evolution of the KS phenotype in this case. After active skin blistering in early childhood, the skin fragility improved, and the course of the disease was relatively mild. At the age of 18, our patient had no blisters, similarly to other KS patients described in the literature. The skin fragility aggravated with age, however.^{Ban et al (1996)} reported a KS patient with recurrence of blisters in the fifth decade. In our case, palmoplantar keratoderma and webbing progressed to distinct contractures and together with photosensitivity represented a worsening symptom, whereas the involvement of the mucous membranes seemed stable. When the genetic basis of KS is disclosed in more families worldwide, it will be interesting to observe genotype-phenotype correlations at clinical and cell biologic level in order to understand the pathomechanisms leading to the various symptoms of KS.

Clinical and morphologic differentiation of KS from other rare diseases can be difficult. A type of epidermolysis bullosa is the most frequent misinterpretation of the diagnosis in these patients, unless photosensitivity and extensive poikiloderma are recognized (^{Shimizu et al, 1997}). In our case, EBS-MP was considered, as the picture of mottled pigmentation was prominent and photosensitivity mild. The phenotypes of the two entities can resemble each other so strongly that^{Gorlin (1984, citation from OMIM}) was convinced that KS is identical with EBS-MP.

From the biologic point of view, the similarity of KS and EBS-MP is intriguing. In both disorders the linkage between the cytoskeleton and the cell membrane is impaired. In KS, a linker protein is functionally defective, in EBS-MP a cytoskeletal component, keratin 5. Kindlin-1 is thought to mediate the connection between the actin cytoskeleton and the cell membrane, and keratin 5 is an essential component of the keratin filaments that are attached to the cell membrane by hemidesmosomal proteins, such as plectin or BP230. Several precedents exist for similar phenotypes caused by mutations in genes encoding for functionally related molecules in multiprotein complexes.