A novel mutation in the 1A domain of keratin 2e in ichthyosis bullosa of Siemens

The stratum corneum: the rampart of the mammalian body

BACKGROUND

The stratum corneum (SC) is the outermost region of the epidermis and plays key roles in cutaneous barrier function in mammals. The SC is composed of 'bricks', represented by flattened, protein-enriched corneocytes, and 'mortar', represented by intercellular lipid-enriched layers. As a result of this 'bricks and mortar' structure, the SC can be considered as a 'rampart' that encloses water and solutes essential for physiological homeostasis and that protects mammals from physical, chemical and biological assaults.

STRUCTURES AND FUNCTIONS

The corneocyte cytoskeleton contains tight bundles of keratin intermediate filaments aggregated with filaggrin monomers, which are subsequently degraded into natural moisturizing compounds by various proteases, including caspase 14. A cornified cell envelope is formed on the inner surface of the corneocyte plasma membrane by transglutaminase-catalysed cross-linking of involucrin and loricrin. Ceramides form a lipid envelope by covalently binding to the cornified cell envelope, and extracellular lamellar lipids play an important role in permeability barrier function. Corneodesmosomes are the main adhesive structures in the SC and are degraded by certain serine proteases, such as kallikreins, during desquamation.

CLINICAL RELEVANCE

The roles of the different SC components, including the structural proteins in corneocytes, extracellular lipids and some proteins associated with lipid metabolism, have been investigated in genetically engineered mice and in naturally occurring hereditary skin diseases, such as ichthyosis, ichthyosis syndrome and atopic dermatitis in humans, cattle and dogs.

Comparative salivary proteomics of cleft palate patients

OBJECTIVES

To investigate salivary proteins with proteomic technologies to evaluate protein composition differences between samples with cleft lip and palate and healthy controls.

DESIGN, PARTICIPANTS

Matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI TOF/TOF) mass spectrometry was used as a high-throughput analytical technique for identification of nonsyndromic cleft lip and palate stimulated salivary proteins. The samples consisted of two groups: 31 cleft lip and palate patients and a control group with 20 healthy volunteers.

RESULTS

The presence of cleft lip and palate stimulated the expression of several proteins, included adaptor-related protein complex 3, dermokine, nidogen 1 precursor, transforming growth factor-β3, and a zinc finger RAN-binding domain containing 2.

CONCLUSIONS

The salivary proteome of cleft lip and palate patients differs from the protein composition of healthy control saliva samples. Several common secreted proteins such as actins, salivary cystatins, and keratins were upregulated by cleft; increased levels of TGF-β3 and dermokine were detected in the pathologic samples. The current proteomic results suggest keratinocyte activation among patients with cleft lip and palate. The score of our preliminary results suggests the hypothesis that identified salivary proteins are of vital clinical importance in tissue regeneration and the molecular repair mechanism seen in patients with cleft lip and palate.

A novel mutation in the 2B domain of keratin 2e causing ichthyosis bullosa of Siemens

Ichthyosis bullosa of Siemens (IBS; MIM: 146800) is an autosomal dominant disorder of keratinization characterized by epidermolytic hyperkeratosis without erythroderma. The clinical features are less marked than those of bullous congenital ichthyosiform erythroderma with relatively mild hyperkeratosis usually limited to the skin flexures. Mutations in the epithelial cytokeratin 2e (K2e), which is expressed in a differentiation-specific fashion in the upper spinous and granular layers of the epidermis, have been shown to cause IBS. We detected a novel mutation in a three generation kindred with IBS (1448T-->A) within exon 7 of the KRT2E gene. This is predictive of an I483N substitution in the 2B domain of K2e. This extends the range of mutations reported to date and illustrates the usefulness of molecular genetics in the diagnosis of this disorder.

Novel point mutations in the steroid sulfatase gene in patients with X-linked ichthyosis: transfection analysis using the mutated genes

X-linked ichthyosis is caused by steroid sulfatase deficiency which results from abnormalities in its coding gene. The majority of X-linked ichthyosis patients ( approximately 90%) have complete or partial deletions of the steroid sulfatase gene. In this study, we examined the mutations of the steroid sulfatase gene in two unrelated X-linked ichthyosis patients without complete deletion of the gene. Polymerase chain reaction-single-strand conformation polymorphism and direct sequencing analyses showed that each patient has a different single base pair substitution within exon 8 encoding the C-terminal half of the steroid sulfatase polypeptide. Both mutations resulted in the transversion of functional amino acids: a G-->C substitution at nucleotide 1344, causing a predicted change of a glycine to an arginine, and a C-->T substitution at nucleotide 1371, causing a change from a glutamine to a stop codon. In vitro steroid sulfatase cDNA expression using site-directed mutagenesis revealed that these mutations are in fact pathogenic and reflect the levels of steroid sulfatase enzyme activities in each of the X-linked ichthyosis patients.

A novel asparagine-->aspartic acid mutation in the rod 1A domain in keratin 2e in a Japanese family with ichthyosis bullosa of Siemens

Ichthyosis bullosa of Siemens is a unique type of congenital ichthyosis characterized by mild hyperkeratosis over the flexural areas and blister formation after mechanical trauma and superficial denuded areas in the hyperkeratotic skin. Recently, mutations in the helix initiation or termination motifs of keratin 2e (KRT2E) have been described in ichthyosis bullosa of Siemens patients. The majority of the mutations reported to date lie in the 2B region. We report a novel amino acid substitution mutation (asparagine-->aspartic acid) in codon 192 at the conserved 1A helix initiation site of the rod domain of KRT2E in a Japanese family with ichthyosis bullosa of Siemens. Our data indicate aspartic acid substitution in codon 192 in the 1A helix initiation site is deleterious to keratin filament network integrity and leads to ichthyosis bullosa of Siemens phenotype.