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1/45. An asparagine to threonine substitution in the 1A domain of keratin 1: a novel mutation that causes epidermolytic hyperkeratosis.

    Epidermolytic hyperkeratosis (EHK) is a congenital, autosomal dominant disorder of cornification characterized by hyperkeratosis and blister formation. The clinical manifestations are heterogeneous, with respect to the extent of body surface involvement, palmar and plantar hyperkeratosis and the presence of erythroderma. Point mutations in the genes encoding the suprabasal-specific keratins, keratins 1 and 10 have been identified in EHK patients. The inappropriate amino acid substitutions cause a collapse of the keratin filament network, resulting in cytolysis of the involved keratinocytes. We report a severe case of EHK with a single base pair mutation that causes a threonine for asparagine substitution in residue 8 (N8T) of the 1A region of the keratin 1 protein. This is the region involved in molecular overlaps between neighboring keratin heterodimers. These findings suggest that even conservative amino acid substitutions in overlap regions can cause tonofilament clumping. ( info)

2/45. ichthyosis bullosa of siemens: report of a family with evidence of a keratin 2e mutation, and a review of the literature.

    We report a large family with ichthyosis bullosa of siemens (IBS) including eight affected members spanning three generations. The classical features of the disease were consistently observed with blistering, superficial peeling of the skin, and localized lichenified hyperkeratosis mainly confined to the limbs. Phenotypic variation, however, was also observed with some individuals exhibiting unusual clinical features. Specifically, the index patient was erythrodermic at birth; she subsequently developed a widespread pustular eruption. Erythroderma is classically absent in IBS and pustulation is very unusual. She also had hypertrichosis of the limbs, as did an affected female first cousin. This has not previously been reported in IBS. Electron microscopy showed complex aggregates of keratin in the spinous and granular layers associated, in places, with remarkably little cell lysis. Sequencing of genomic dna revealed a mutation (E493K) in keratin 2e. A review of the literature on IBS indicates that E493K is the most commonly reported mutation to date and might represent a mutational hotspot for this disease. ( info)

3/45. ichthyosis bullosa of siemens resulting from a novel missense mutation near the helix termination motif of the keratin 2e gene.

    ichthyosis bullosa of siemens (IBS) is an autosomal dominant disorder of keratinization. It is characterized by a mild epidermolytic ichthyosis which tends to localize to the flexures. Affected individuals are born with widespread blistering, which develops into large hyperkeratotic plaques over the extremities. Mutations in the K2e gene cause epidermolytic hyperkeratosis confined to the upper spinous and granular layers, as observed in IBS. In this report, we describe a novel mutation in the keratin 2e gene in a four-generation IBS kindred of German ancestry. The mutation resides within the 2B helix termination motif of the keratin 2e gene, and extends the body of evidence implicating keratin 2e gene mutations in IBS. ( info)

4/45. Epidermolytic hyperkeratosis with polycyclic psoriasiform plaques resulting from a mutation in the keratin 1 gene.

    Epidermolytic hyperkeratosis (EHK) is a genodermatosis caused by mutations in either the keratin 1 (K1) or keratin 10 (K10) genes, and characterized by erythroderma and blistering at birth, with development of a ribbed, ichthyotic hyperkeratosis and palmoplantar keratoderma. A wide variety of mutations within the highly conserved helix termination motifs of the central rod domains of the K1 or K10 genes correlate with the highly variable phenotypic severity observed in EHK. We report a unique EHK-like phenotype exhibiting autosomal dominant inheritance with variable expressivity in four affected individuals in a single family. Clinically, affected individuals manifest transient blistering at birth followed by chronic diffuse palmoplantar keratoderma without transgradiens. Intermittent flares of non-migratory polycylic erythematous psoriasiform plaques which worsen and abate in severity were present in all affected individuals, but showed immense individual variation in both severity and duration, ranging from weeks to months. Histopathologic examination of the psoriasiform plaques demonstrated the characteristic features of EHK. Sequencing of the K1 gene in affected family members revealed a heterozygous A-to-T transversion at nucleotide 1435 within exon 7, converting isoleucine (ATT) to phenylalanine (TTT), (I479F). The mutation resides within the highly conserved helix termination motif of the helix 2B segment of the K1 gene. This unique clinical phenotype and the associated K1 mutation have not been previously described, and it is referred to here as EHK with polycyclic, psoriasiform plaques (EHK/PPP). ( info)

5/45. Bullous ichthyosiform erythroderma, developmental delay, aortic and pulmonary stenosis in association with a FRA12A.

    We present an 11-year-old female with bullous ichthyosiform erythroderma (BIE), learning disability, patent ductus arteriosus and mild stenosis of the aortic and pulmonary arteries. Chromosome analysis showed the expression of the rare folate-sensitive fragile site FRA12A at 12q13 in 8/20 (40%) of blood lymphocytes cultured in folate-deficient medium in the presence of trimethoprim. Her mother and maternal grandmother are phenotypically normal, but her mother shows expression of the same fragile site in 4/20 (20%) of cells cultured under the same conditions. lymphocytes from the grandmother only showed expression of the fragile site when cultured in the presence of methotrexate in folate deficient medium. Interestingly, two genes (keratin 1 and keratin 2e) which are known to cause BIE map to 12q13. Molecular data is presented excluding three candidate (CCG)n repeats within keratin 1 gene. We present a review of previously reported FRA12A cases and discuss possible molecular explanations for the clinical findings in this patient. ( info)

6/45. New mutations in keratin 1 that cause bullous congenital ichthyosiform erythroderma and keratin 2e that cause ichthyosis bullosa of siemens.

    The intermediate filaments of epithelial cells are formed by keratins, a family of structurally related proteins, which are expressed in pairs of acidic (type I) and basic (type II) polypeptides in a tissue- and differentiation-specific manner. Mutations in the genes encoding several keratins have been implicated in the pathogenesis of diseases of keratinization. We report molecular analysis of two patients with the rare autosomal dominant disorders bullous congenital ichthyosiform erythroderma (BCIE) and ichthyosis bullosa of siemens (IBS). Previous studies have shown that these genodermatoses are due to mutations in the KRT1 and KRT2E genes, respectively. We report a new amino acid substitution mutation in codon 155 of KRT1 (valine to aspartic acid) in the conserved H1 domain of the protein in the patient with BCIE. We also report a novel amino acid substitution mutation in codon 192 of KRT2E (asparagine to lysine) in the conserved 1A helix initiation peptide of the protein in the patient with IBS. Our results demonstrate that these mutations are deleterious to keratin filament network stability and lead to specific clinical inherited disorders of keratinization. ( info)

7/45. Phenotypic heterogeneity in bullous congenital ichthyosiform erythroderma: possible somatic mosaicism for keratin gene mutation in the mildly affected mother of the proband.

    BACKGROUND: Bullous congenital ichthyosiform erythroderma (BCIE) shows phenotypic variability. An epidermal nevus may represent somatic mosaicism for keratin gene mutation, which produces generalized BCIE in the next generation. This fact provides evidence that a postzygotic mutation can be passed on to the next generation in BCIE. We hypothesized that the same phenomenon occurred in a family with BCIE whose phenotypes were extremely different. OBSERVATIONS: We studied a 19-year-old boy with severe ichthyosiform erythroderma and prominent palmoplantar hyperkeratosis with digital contracture. In contrast, the proband's mother exhibited only mild ichthyosiform skin, granular verrucous lesions, and less severe streaky palmoplantar hyperkeratosis. mutation analysis in the proband showed a keratin K1 mutation (N187S, ie, an A-to-G transition at the second position of codon 187, resulting in an asparagine-to-serine substitution). In the mother, the same keratin gene mutation was recognized, but only faintly in the leukocyte dna, indicating that the amount of the mutated allele in leukocyte dna was very low compared with that from the proband. CONCLUSIONS: We speculate that the mildly affected mother showed keratin 1 gene mosaicism, and that the BCIE phenotype had been transmitted in a severe form through a mechanism that passes the keratin gene mutation to the next generation. These results suggest that mild forms of BCIE may actually represent extensive epidermal nevi/keratin gene mosaicism. ( info)

8/45. Bullous and non-bullous ichthyosiform erythroderma associated with generalized pustular psoriasis of von Zumbusch type.

    Bullous ichthyosiform erythroderma (BIE) and non-bullous ichthyosiform erythroderma (NBIE) are rare congenital ichthyoses. Generalized pustular psoriasis (GPP) of von Zumbusch type is a rare and severe form of psoriasis marked by desquamative and pustular erythroderma associated with fever and altered general conditions. We report two adults with an ichthyosis typical of BIE in the first case and NBIE in the second, without any previous history of psoriasis, who presented with a severe and relapsing GPP of von Zumbusch type. Using current knowledge of the genetic relationship between psoriasis and congenital ichthyoses, we discuss the possibility of a common physiopathological link between congenital ichthyoses and GPP, and examine the possible therapeutic problems resulting from this pathological association, especially in BIE. ( info)

9/45. A keratin 10 gene mutation (Arg156Cys) in a Japanese patient with bullous congenital ichthyosiform erythroderma.

    We described a 19-year old Japanese female with bullous congenital ichthyosiform erythroderma (BCIE) and examined the keratin gene mutation. physical examination disclosed generalized erythema, ichthyosiform skin with scales, and erosions without palmoplantar keratoderma. Histological examination revealed hyperkeratosis with vacuolar degeneration in the granular layer of the epidermis. sequence analysis demonstrated a C to G transition at the first position of codon 156 in the keratin 10 gene. The amino acid at codon 156 was deduced to have changed from arginine to cystine. Substitution from arginine to cysteine at codon 156 of the K 10 gene is assumed to be fatal for keratin filament assembly regardless of racial or ethnic difference. ( info)

10/45. HID and KID syndromes are associated with the same connexin 26 mutation.

    BACKGROUND: keratitis-ichthyosis-deafness (KID) syndrome is a debilitating ectodermal dysplasia that predisposes patients to develop squamous cell carcinomas in addition to leading to profound sensory deafness and erythrokeratoderma. We recently demonstrated that KID can be caused by a specific missense mutation in connexin 26 (GJB2). Another syndrome, called hystrix-like ichthyosis-deafnesss (HID) syndrome, strongly resembles the KID syndrome. These disorders are distinguished mainly on the basis of electron microscopic findings. We hypothesized that KID and HID syndromes may be genetically related. OBJECTIVE: To demonstrate by mutation analysis that HID and KID syndromes are genetically indistinguishable. methods: dna was extracted from paraffin-embedded tissue samples of the first HID syndrome patient described in the literature. Since the KID syndrome mutation abolishes an AspI restriction site, we were able to screen the patient's dna by polymerase chain reaction and subsequent restriction enzyme analysis. RESULTS: Restriction analysis of the connexin 26 gene in HID syndrome demonstrated the presence of the KID syndrome mutation that we previously described. This result was confirmed by direct dna sequencing. CONCLUSIONS: We show that KID and HID syndromes are identical at the molecular level and confirm the clinical impression that these syndromes are one and the same. That previous clinical reports made a distinction may be a consequence of sampling artefacts; alternatively, genetic background effects such as the presence of concurrent mutations in other skin-expressed genes may modify the phenotype. ( info)
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