[Diverse mechanisms of itch]

Itch is known to be a sensation that provokes a desire to scratch. It is a bio-warning sensation, which serves to detect and remove parasites and irritants in the superficial layers of the skin and the mucous membrane. The mechanisms of itch are not simple. It is mediated by mast cells and keratinocytes, which each produce and release a few itch mediators. Alterations in the distribution of primary afferent fibers in the epidermis are also involved in itch. Agents that have a wide spectrum of inhibitory action on mast cells, keratinocytes and primary afferents may be needed to effectively suppress itch.

[The so-called dry skin of the diabetic patient]

Rough skin or xerosis, known by the laity as dry skin, results from a defect in the stratum corneum desquamation which normally remains imperceptible. This condition is negatively influenced by winter climatic conditions. Atopic dermatitis and trophic changes related to post-menopause, ageing, diabetes mellitus, as well as other endrocrine and metabolic disturbances are also involved in this process. Xerosis can be improved at various degrees by emollients, humectants, hydrating agents and squamolytic agents.

Pathophysiologic basis for growth failure in children with ichthyosis: an evaluation of cutaneous ultrastructure, epidermal permeability barrier function, and energy expenditure

OBJECTIVE

Because an impaired epidermal permeability barrier is present in many of the ichthyoses, we examined the contribution of barrier failure to caloric requirements in children with ichthyosis and growth failure.

STUDY DESIGN

Transepidermal water loss (TEWL) and ultrastructural parameters of the permeability barrier were evaluated in 10 hospitalized children with ichthyosis and growth failure. Nutritional intake, resting energy expenditure, and calories lost as heat of evaporation were determined.

RESULTS

Mean basal TEWL rates were markedly elevated in all study patients in comparison to the expected upper limit of normal (39.6+/-20.6 vs 8.7 mL/m(2) per hour). The severity of abnormalities in the ultrastructure of permeability barrier-related structures, assessed semiquantitatively, correlated significantly to mean basal TEWL rates (P <.001). Total body daily TEWL was elevated (746 +/- 468 vs 209 mL/d), resulting in a caloric drain of 433 +/- 272 kcal/d (21 +/- 9.8 kcal/kg per day) through heat of evaporation. Nutrient intake exceeded requirements in all, but resting energy expenditure exceeded predicted in 5 of 6 patients and correlated significantly with mean basal TEWL rates (P <.005).

CONCLUSIONS

A defective permeability barrier in children with ichthyosis can result in ample chronic losses of water and calories to impair growth.

Nutritional status and gastrointestinal structure and function in children with ichthyosis and growth failure

Growth failure occurs in several of the ichthyoses, a heterogeneous group of inherited disorders characterized by thickened or scaly skin. This suggests that there may be common pathogenic mechanisms causing failure to thrive. Previous studies have proposed that a hypermetabolic state induced by epidermal inflammation and hyperproliferation or enteropathy leading to malabsorption and nutritional deficiencies might account for the growth failure in icthyosis.

OBJECTIVE

The purpose of this study was to examine the extent of enteropathy and nutritional deficiency in children with severe ichthyosis and growth failure.

METHODS

Ten children with different types of ichthyoses and growth failure were studied.

RESULTS

Evaluation of gastrointestinal structure and function revealed few abnormalities other than mild fat malabsorption in two patients. Total caloric intake exceeded established requirements for age, height, and weight in all patients. Deficiencies of fat-soluble vitamins were identified in a few subjects. Mild elevations in total calcium and magnesium blood level, elevated hematocrit levels, and constipation were observed in many patients.

CONCLUSIONS

Nutritional deficiencies and gastrointestinal abnormalities are uncommon in children with ichthyosis and failure to thrive. Chronic hypovolemia caused by impaired epidermal permeability barrier may be common in this population.

Conséquences fonctionnelles des perturbations des lipides cutanés

Epidermal lipids constitute an ultimate frontier between the organism and its environment. Their essential role consists of providing a barrier limiting both transepidermal water loss and penetration of external factors, such as irritants. Efficacy of the barrier depends on the physicochemical properties of the substance applied to the skin surface and the increase in transepidermal water loss, which may be quantified, is proportional to the provoked perturbation in the barrier function. In atopic dermatitis epidermis, a significant decrease in the ceramide content and abnormally low levels of omega-6 fatty acids correlate with an increased rate of water loss at the skin surface--a sign of an impaired barrier. However, similar signs are observed in the atrophic epidermis provoked by long term local corticotherapy. Epidermal lipid profiles are also seriously modified in various ichthyoses, and are partially responsible for the hyperkeratosis observed clinically, e.g.: the recessive X-linked form is provoked by a mutation of the steroid sulphatase gene and the resulting accumulation of unconverted precursor of cholesterol. Modification of the lipid composition in acne contributes to comedo formation, whereas UV improves barrier function (and may provoke hyperkeratosis) through an increase in the stratum corneum lipid content. Another source of lipids at the epidermal surface is sebaceous glands. Waxes present in the sebum increase friction coefficient of the skin surface. Sebum also influences (decreases) the rate of penetration of lipophilic substances applied on the skin. Its role in the skin biology appears to be less vital than that of the lipids constituting the permeability barrier of the stratum corneum.

The development and initial validation of the Liverpool sicca index to assess symptoms and dysfunction in patients with primary Sjögren's syndrome

BACKGROUND

A validated measure to assess sicca-related symptoms in patients with primary Sjögren's syndrome (1 degrees SS) is required for clinical studies.

METHODS

A self-administered questionnaire was developed to assess sicca-related symptoms and dysfunction in 1 degrees SS. This was administered to three groups of 40 respondents to measure construct validity: 1 degrees SS patients, non-SS patients reporting xerostomia and a non-patient group. The frequency of scores and the mean score for each question were calculated for each group. Reliability was assessed by test/retest.

RESULTS

The measure consisted of 28 items divided into five domains. Scores for questions in domains were generally worse (higher) for 1 degrees SS patients than for patients with xerostomia. The non-patient group reported the best (lowest) scores for all questions. The Kappa statistic for all but four questions was greater than 0.6, suggesting good reliability.

CONCLUSION

Questionnaire showed good construct validity and reliability. The Liverpool sicca index needs to be further validated in larger, multicentre studies.

Development of ichthyosiform skin compensates for defective permeability barrier function in mice lacking transglutaminase 1

Transglutaminase 1 (TGase 1) is one of the genes implicated in autosomal recessive congenital ichthyosis. Skin from TGase 1(-/-) mice, which die as neonates, lacks the normal insoluble cornified envelope and has impaired barrier function. Characterization of in situ dye permeability and transepidermal water loss revealed defects in the development of the skin permeability barrier in TGase 1(-/-) mice. In the stratum corneum of the skin, tongue, and forestomach, intercellular lipid lamellae were disorganized, and the corneocyte lipid envelope and cornified envelope were lacking. Neonatal TGase 1(-/-) mouse skin was taut and erythrodermic, but transplanted TGase 1(-/-) mouse skin resembled that seen in severe ichthyosis, with epidermal hyperplasia and marked hyperkeratosis. Abnormalities in those barrier structures remained, but transepidermal water loss was improved to control levels in the ichthyosiform skin. From these results, we conclude that TGase 1 is essential to the assembly and organization of the barrier structures in stratified squamous epithelia. We suggest that the ichthyosiform skin phenotype in TGase 1 deficiency develops the massive hyperkeratosis as a physical compensation for the defective cutaneous permeability barrier required for survival in a terrestrial environment.

Transglutaminases in disease

Transglutaminases (TGases) are enzymes that are widely used in many biological systems for generic tissue stabilization purposes. Mutations resulting in lost activity underlie several serious disorders. In addition, new evidence documents that they may also be aberrantly activated in tissues and cells and contribute to a variety of diseases, including neurodegenerative diseases such as Alzheimer's and Huntington's diseases. In these cases, the TGases appear to be a factor in the formation of inappropriate proteinaceous aggregates that may be cytotoxic. In other cases such as celiac disease, however, TGases are involved in the generation of autoantibodies. Further, in diseases such as progressive supranuclear palsy, Huntington's, Alzheimer's and Parkinson's diseases, the aberrant activation of TGases may be caused by oxidative stress and inflammation. This review will examine the role and activation of TGases in a variety of diseases.

[Xerosis]

The clinical characteristic of xerosis is rough or coarse skin. Physiopathologically, the structure of the stratum corneum is modified and abnormalities in keratinization, proliferation, surface lipid, water metabolism and also pH and sebum exist. There are two forms of xerosis: dry skin forms and ichtyosis or ichtyosis-like forms. Xerosis has many etiologies including external aggression, senescence, drugs, infection, atopy, deficiencies, malignant diseases, endocrine affections, eating disorders and renal failure in dialyzed patients. It provokes cutaneous discomfort and unaesthetic appearance that justify appropriate treatment. Treatment is essentially local, symptomatic and must be accompanied by general measures. Many products include moisturizers and emollients (keratolytics: salicylic acid, urea and alpha-hydroxy acid).

Environmental effects on the functions of the stratum corneum

The stratum corneum (SC) is such an efficient barrier that only 2-5 g per h per cm2 of transepidermal water loss (TEWL) occurs in normal skin. The SC also plays another important role at the skin surface in keeping our skin smooth and flexible by binding water. We exposed a simulation model of in vivo SC to various, excessive physical insults in vitro, such as irradiation with 1 J per cm2 of UVB, 50 J per cm2 of UVA, or 3000 rad of X-ray, heating at 90 degrees C for 3 min, freezing at -196 degrees C for 60 s or repeated placement in an extremely dry or humid condition. None of them could cause any permanent change in the SC functions. Only the application of chemical agents such as lipid solvents or a detergent or the affliction of trauma resulted in a functional derangement of the SC. Because the viable skin tissues are more vulnerable to the effects of the environment than the SC, most of the abnormalities of the SC functions developing after environmental insults are secondarily caused by enhanced epidermal proliferation induced under the influence of underlying inflammation. These functional abnormalities were found to be demonstrable with biophysical measurements long after the disappearance of skin redness, the clinically observable sign of inflammation. The SC abnormalities in inflamed skin are also detectable as a change in the content of chemical mediators. For example, the ratio between proinflammatory IL-1 and its receptor antagonist (IL-1ra) whose production by epidermal keratinocytes is markedly enhanced by various proinflammatory stimuli, showed a deviation towards an excess of the latter in inflammatory skin. Facial skin that is always exposed to the environment is unique in that its SC shows such a deviation in the IL-1/IL-1ra ratio suggestive for the presence of mild inflammation even in normal individuals.

Identification, by homozygosity mapping, of a novel locus for autosomal recessive congenital ichthyosis on chromosome 17p, and evidence for further genetic heterogeneity

Autosomal recessive congenital ichthyosis (ARCI) comprises a group of severe disorders of keratinization, characterized by variable erythema and skin scaling. It is known for its high degree of genetic and clinical heterogeneity. Mutations in the gene for keratinocyte transglutaminase (TGM1) on chromosome 14q11 were shown in patients with ARCI, and a second locus was described, on chromosome 2q, in families from northern Africa. Three other loci for ARCI, on chromosomes 3p and 19p, were identified recently. We have embarked on a whole-genome scan for further loci for ARCI in four families from Germany, Turkey, and the United Arab Emirates. A novel ARCI locus was identified on chromosome 17p, between the markers at D17S938 and D17S1856, with a maximum LOD score of 3.38, at maximum recombination fraction 0.00, at D17S945, under heterogeneity. This locus is linked to the disease in the Turkish family and in the German family. Extensive genealogical studies revealed that the parents of the German patients with ARCI were eighth cousins. By homozygosity mapping, the localization of the gene could then be refined to the 8.4-cM interval between D17S938 and D17S1879. It could be shown, however, that ARCI in the two Arab families is linked neither to the new locus on chromosome 17p nor to one of the five loci known previously. Our findings give evidence of further genetic heterogeneity that is not linked to distinctive phenotypes.

Evidence for novel functions of the keratin tail emerging from a mutation causing ichthyosis hystrix

Unraveling the molecular basis of inherited disorders of epithelial fragility has led to understanding of the complex structure and function of keratin intermediate filaments. Keratins are organized as a central alpha-helical rod domain flanked by nonhelical, variable end domains. Pathogenic mutations in 19 different keratin genes have been identified in sequences corresponding to conserved regions at the beginning and end of the rod. These areas have been recognized as zones of overlap between aligned keratin proteins and are thought to be crucial for proper assembly of keratin intermediate filaments. Consequently, all keratin disorders of skin, hair, nail, and mucous membranes caused by mutations in rod domain sequences are characterized by perinuclear clumping of fragmented keratin intermediate filaments, thus compromising mechanical strength and cell integrity. We report here the first mutation in a keratin gene (KRT1) that affects the variable tail domain (V2) and results in a profoundly different abnormality of the cytoskeletal architecture leading to a severe form of epidermal hyperkeratosis known as ichthyosis hystrix Curth-Macklin. Structural analyses disclosed a failure in keratin intermediate filament bundling, retraction of the cytoskeleton from the nucleus, and failed translocation of loricrin to the desmosomal plaques. These data provide the first in vivo evidence for the crucial role of a keratin tail domain in supramolecular keratin intermediate filament organization and barrier formation.

Efficacy of urea therapy in children with ichthyosis. A multicenter randomized, placebo-controlled, double-blind, semilateral study

BACKGROUND

Ichthyoses are genetic disorders of keratinization which are uncomfortable due to their conspicuous scaling, itching and cosmetic problems. Especially in childhood, ichthyoses can lead to social discrimination and psychological problems. Efficient therapies are necessary which are safe and well tolerated.

OBJECTIVE

The aim of the study was to investigate the keratolytic and moisturizing properties as well as the tolerance of a new urea lotion when applied to hyperkeratotic and ichthyotic skin in childhood.

METHODS

The study was conducted as a multicenter, randomized, placebo-controlled, double-blind, semilateral investigation. Sixty children between 1 and 16 years treated one side of the most affected extremity with Laceran 10% urea lotion for 8 weeks. On the other side the urea-free Laceran lotion base was given. On each side of the body a control area was left untreated. The investigators evaluated the global severity of ichthyotic symptoms with the help of a visual analogue scale.

RESULTS

The analysis of the global estimation of severity of ichthyosis showed improvements being stronger in the body areas treated with Laceran 10% urea lotion (from 4.8 to 2.0 points) than in the areas treated with the urea-free Laceran lotion base (from 4.8 to 2.5 points). The response rates were 65% after 4 weeks and 78% after 8 weeks for Laceran 10% urea lotion, 50% after 4 weeks and 72% after 8 weeks for the urea-free Laceran lotion base.

CONCLUSION

It can be ascertained that Laceran 10% urea lotion has a strong positive effect on generalized ichthyotic keratinization disorders.

Localization of the Netherton syndrome gene to chromosome 5q32, by linkage analysis and homozygosity mapping

Netherton syndrome (NS [MIM 256500]) is a rare and severe autosomal recessive disorder characterized by congenital ichthyosis, a specific hair-shaft defect (trichorrhexis invaginata), and atopic manifestations. Infants with this syndrome often fail to thrive; life-threatening complications result in high postnatal mortality. We report the assignment of the NS gene to chromosome 5q32, by linkage analysis and homozygosity mapping in 20 families affected with NS. Significant evidence for linkage (maximum multipoint LOD score 10.11) between markers D5S2017 and D5S413 was obtained, with no evidence for locus heterogeneity. Analysis of critical recombinants mapped the NS locus between markers D5S463 and D5S2013, within an <3.5-cM genetic interval. The NS locus is telomeric to the cytokine gene cluster in 5q31. The five known genes encoding casein kinase Ialpha, the alpha subunit of retinal rod cGMP phosphodiesterase, the regulator of mitotic-spindle assembly, adrenergic receptor beta2, and the diastrophic dysplasia sulfate-transporter gene, as well as the 38 expressed-sequence tags mapped within the critical region, are not obvious candidates. Our study is the first step toward the positional cloning of the NS gene. This finding promises a better understanding of the molecular mechanisms that control epidermal differentiation and immunity.

The pathogenesis of severe congenital ichthyosis of the neonate

Severe congenital ichthyosis of the neonate include several major subtypes, i.e. harlequin ichthyosis, lamellar ichthyosis (LI), and congenital ichthyosiform erythroderma. Knowledge of the pathogenetic mechanisms is significant for the precise diagnosis, treatment, genetic counseling and prenatal diagnosis. This article reviews recent advances in studies on genetic defects and pathogenetic mechanisms of these severe congenital ichthyosis and, in addition, discuss the feasibility and methods of their prenatal diagnosis. Recently, reduced activity of the serine/threonine protein phosphatase in keratinocytes was suggested to be the cause of harlequin ichthyosis. In some families of LI, transglutaminase 1 gene mutations were identified as causative genetic defects and transglutaminase 1 is thought to be one of the candidate molecules for non-bullous congenital ichthyosiform erythroderma (NBCIE). Genotype/phenotype correlation in bullous congenital ichthyosis is now being clarified. Mutations within the rod domain, not in the beginning or the end of the rod domain, of keratin 10 were reported in annular epidermolytic ichthyosis (AEI), the distinct subtype of bullous congenital ichthyosiform erythroderma.

Association in the same patient of autosomal dominant progressive external ophthalmoplegia with multiple mtDNA deletions and X-linked ichthyosis: clinical, biochemical, histological, submicroscopic and molecular genetic study

Autosomal dominant chronic progressive external ophthalmoplegia (AdPEO) is a muscle mitochondrial disorder due to multiple large scale rearrangements of the mitochondrial DNA. This disorder is probably due to a nuclear defect which causes genetic instability or an impairment in the replication of mitochondrial DNA. X-linked ichthyosis (XLI) is a skin disorder caused by a deletion in the steroid-sulphatase gene. Here we report the clinical, biochemical, morphologic and molecular genetic findings in a patient affected by both AdPEO, inherited by the father, and steroid-sulphatase-deficiency, inherited by the mother. The association in the same patient of the two inherited diseases is merely casual and does not seem to influence the phenotypic expression of the two diseases.

Genetic skin diseases

Recent advances in molecular genetics have led to major breakthroughs in the understanding of two heterogeneous groups of inherited skin diseases, epidermolysis bullosa and the ichthyoses. Mutations in keratins K5 or K14 are found in epidermolysis bullosa simplex. The gravis (Herlitz) variety of junctional epidermolysis bullosa is characterized by defects in the anchoring filament protein kalinin. Both dominant and recessive forms of dystrophic epidermolysis bullosa appear to be due to mutations in the type VII collagen gene. Biochemical studies in patients with ichthyosis vulgaris reveal that the proteins profilaggrin and filaggrin are reduced or absent. Recessive X-linked ichthyosis is characterized by a deficiency of the enzyme steroid sulfatase. A type of lamellar ichthyosis may be explained on the basis of abnormal cornified cell envelope formation, and bullous congenital ichthyosiform erythroderma (epidermolytic hyperkeratosis) is caused by mutations in keratins K1 or K10.