Association of arterial stiffness with aortic calcification and tortuosity

Impact of arterial stiffness on aortic morphology has not been well evaluated. We sought to investigate the association of brachial-ankle pulse wave velocity (baPWV) with aortic calcification and tortuosity.A total of 181 patients (65.4 ± 10.4 years, males 59.7%) who underwent computed tomographic angiography and baPWV measurement within 1 month of study entry were retrospectively reviewed. Aortic calcification was quantified by the calcium scoring software system. Aortic tortuosity was defined as the length of the midline in the aorta divided by the length of linear line from the aortic root to the distal end of the thoraco-abdominal aorta. In simple correlation analyses, baPWV was correlated with aortic calcification (r = 0.36, P < .001) and tortuosity (r = 0.16, P = .030). However, these significances disappeared after controlling for confounders in multivariate analyses. Factors showing an independent association with aortic calcification were age (β = 0.37, P < .001), hypertension (β = 0.19, P = .003), diabetes mellitus (β = 0.12, P = .045), smoking (β = 0.17, P = .016), and estimated glomerular filtration rate (β = -0.25, P = .002). Factors showing an independent association with aortic tortuosity were age (β = 0.34, P < .001), body mass index (β = -0.19, P = .018), and diabetes mellitus (β = -0.21, P = .003).In conclusion, baPWV reflecting arterial stiffness was not associated with aortic calcification and tortuosity. Traditional cardiovascular risk factors were more influential to aortic geometry. Further studies with a larger sample size are needed to confirm our results.

Annular Lesions: Diagnosis and Treatment

Annular lesions can present in a variety of diseases. Knowledge of the physical appearance and history of presentation of these skin findings can help in the diagnosis. A pruritic, annular, erythematous patch that grows centrifugally should prompt evaluation for tinea corporis. Tinea corporis may be diagnosed through potassium hydroxide examination of scrapings. Recognizing erythema migrans is important in making the diagnosis of Lyme disease so that antibiotics can be initiated promptly. Plaque psoriasis generally presents with sharply demarcated, erythematous silver plaques. Erythema multiforme, which is due to a hypersensitivity reaction, presents with annular, raised lesions with central clearing. Lichen planus characteristically appears as planar, purple, polygonal, pruritic papules and plaques. Nummular eczema presents as a rash composed of coin-shaped papulovesicular erythematous lesions. Treatment is aimed at reducing skin dryness. Pityriasis rosea presents with multiple erythematous lesions with raised, scaly borders, and is generally self-limited. Urticaria results from the release of histamines and appears as well-circumscribed, erythematous lesions with raised borders and blanched centers. Annular lesions occur less commonly in persons with fixed drug eruptions, leprosy, immunoglobulin A vasculitis, secondary syphilis, sarcoidosis, subacute cutaneous lupus erythematosus, and granuloma annulare.

Acquired and congenital forms of heterotopic ossification: new pathogenic insights and therapeutic opportunities

Heterotopic ossification (HO) involves the formation and accumulation of extraskeletal bone tissue at the expense of local tissues including muscles and connective tissues. There are common forms of HO that are triggered by extensive trauma, burns and other bodily insults, and there are also rare congenital severe forms of HO that occur in children with Fibrodysplasia Ossificans Progressiva or Progressive Osseous Heteroplasia. Given that HO is often preceded by inflammation, current treatments usually involve anti-inflammatory drugs alone or in combination with local irradiation, but are not very effective. Recent studies have provided novel insights into the pathogenesis of acquired and genetic forms of HO and have used the information to conceive and test new and more specific therapies in animal models. In this review, I provide salient examples of these exciting and promising advances that are undoubtedly paving the way toward resolution of this debilitating and at times fatal disease.

The prevalence and clinical manifestation of hereditary thrombophilia in Korean patients with unprovoked venous thromboembolisms

Background

Hereditary thrombophilia (HT) is a genetic predisposition to thrombosis. Asian mutation spectrum of HT is different from Western ones. We investigated the incidence and clinical characteristics of HT in Korean patients with unprovoked venous thromboembolism (VTE).

Methods

Among 369 consecutive patients with thromboembolic event who underwent thrombophilia tests, we enrolled 222 patients diagnosed with unprovoked VTE. The presence of HT was confirmed by DNA sequencing of the genes that cause deficits in natural anticoagulants (NAs). Median follow-up duration was 40±38 months.

Results

Among the 222 patients with unprovoked VTE, 66 (29.7%) demonstrated decreased NA level, and 33 (14.9%) were finally confirmed to have HT in a genetic molecular test. Antithrombin III deficiency (6.3%) was most frequently detected, followed by protein C deficiency (5.4%), protein S deficiency (1.8%), and dysplasminogenemia (1.4%). The HT group was significantly younger (37 [32–50] vs. 52 [43–65] years; P < 0.001) and had a higher proportion of male (69.7% vs. 47%; P = 0.013), more previous VTE events (57.6% vs. 31.7%; P = 0.004), and a greater family history of VTE (43.8% vs. 1.9%; P < 0.001) than the non-HT group. Age <45 years and a family history of VTE were independent predictors for unprovoked VTE with HT (odds ratio, 9.435 [2.45–36.35]; P = 0.001 and 92.667 [14.95–574.29]; P < 0.001).

Conclusions

About 15% of patients with unprovoked VTE had HT. A positive family history of VTE and age <45 years were independent predictors for unprovoked VTE caused by HT.

A 7-year-old with indurated skin and unilateral progressive joint immobility: A case of stiff skin syndrome

Stiff skin syndrome is a rare sclerotic condition that presents during infancy or early childhood. It has an insidious chronic course and may lead to significant co-morbidity and reduced quality of life. Often, affected individuals experience impaired ambulation and immobilization related to joint involvement. Clinically, it may resemble other sclerotic diseases, so histopathological evaluation is necessary to establish a diagnosis. As it is a condition with limited treatment options, prompt diagnosis and early initiation of physical therapy is crucial to prevent joint restriction and maintain quality of life. We describe a case of a 7-year-old with stiff skin syndrome, and review the literature to discuss the clinical presentation, histological findings, and management of this condition.

Actinic Prurigo

Actinic prurigo is an idiopathic photodermatosis that affects the skin, as well as the labial and conjunctival mucosa in indigenous and mestizo populations of Latin America. It starts predominantly in childhood, has a chronic course, and is exacerbated with solar exposure. Little is known of its pathophysiology, including the known mechanisms of the participation of HLA-DR4 and an abnormal immunologic response with increase of T CD4+ lymphocytes. The presence of IgE, eosinophils, and mast cells suggests that it is a hypersensitivity reaction (likely type IVa or b). The diagnosis is clinical, and the presence of lymphoid follicles in the mucosal histopathologic study of mucosa is pathognomonic. The best available treatment to date is thalidomide, despite its secondary effects.

[The coronary arterial tortuosity in workers of vibro-noisy professions and its role in the ischemic damage of the myocardium]

The article is devoted the study of role of the phenomenon of coronal arterial tortuosity in pathogeny of ischemic heart disease. For 89% patients with a cardiac pain and coronal arterial tortuosity at which at a conservative cardiologic inspection it was not discovered signs of organic defeat of heart and coronal vessels, by the high-specific functional methods of research and stress-tests the presence of cardial ischemia is set. Accordance localization of ischemic areas of myocardium is also exposed to the areas of vascularization by the coronal tortuosity arteries. Among all inspected persons with the coronal arterial tortuosity 21.7% belonged to the group of workers the profession of which is related to the combined action of local vibration and industrial noise.

Impact of coronary tortuosity on coronary blood supply: a patient-specific study

BACKGROUND

Tortuous coronary arteries are commonly observed in clinical screenings and it may cause a reduction of the coronary pressure. However, whether this reduction leads to significant decreasing in the coronary blood supply is still unknown. The purpose of this study was to investigate the effect of the coronary tortuosity (CT) on the coronary blood supply.

METHOD

A computational fluid dynamics (CFD) study was conducted to evaluate the impact of tortuosity on the coronary blood supply. Two patient-specific left anterior descending coronary artery (LAD) models and the corresponding non-tortuous models were reconstructed to perform three-dimensional CFD analysis. The lumped parameter model was coupled to the outlet of the simulated branches to represent the absent downstream vasculatures. The rest and exercise conditions were modeled by specifying proper boundary conditions.

RESULT

Under resting condition, the mean flow rate could be maintained by decreasing less than 8% of the downstream vascular bed's resistance for tortuous models. While during exercise (maximal dilatation condition), the maximal coronary blood supply would reduce up to 14.9% due to tortuosity. Assuming that the flow rate can be maintained by the auto-regulation effect under the maximal dilatation condition, the distal resistances for CT models still have to reduce more than 23% to maintain blood perfusion.

CONCLUSIONS

Coronary tortuosity has minor influence on coronary blood supply at rest; while during exercise, patients with CT may lack the ability to adjust distal resistance sufficiently to compensate for the extra resistances generated by tortuosity and this may further lead to an ineffective regulation of the blood supply.

Impact of coronary tortuosity on coronary pressure: numerical simulation study

Background

Coronary tortuosity (CT) is a common coronary angiographic finding. Whether CT leads to an apparent reduction in coronary pressure distal to the tortuous segment of the coronary artery is still unknown. The purpose of this study is to determine the impact of CT on coronary pressure distribution by numerical simulation.

Methods

21 idealized models were created to investigate the influence of coronary tortuosity angle (CTA) and coronary tortuosity number (CTN) on coronary pressure distribution. A 2D incompressible Newtonian flow was assumed and the computational simulation was performed using finite volume method. CTA of 30°, 60°, 90°, 120° and CTN of 0, 1, 2, 3, 4, 5 were discussed under both steady and pulsatile conditions, and the changes of outlet pressure and inlet velocity during the cardiac cycle were considered.

Results

Coronary pressure distribution was affected both by CTA and CTN. We found that the pressure drop between the start and the end of the CT segment decreased with CTA, and the length of the CT segment also declined with CTA. An increase in CTN resulted in an increase in the pressure drop.

Conclusions

Compared to no-CT, CT can results in more decrease of coronary blood pressure in dependence on the severity of tortuosity and severe CT may cause myocardial ischemia.

Loss of Kindlin-1 causes skin atrophy and lethal neonatal intestinal epithelial dysfunction

Kindler Syndrome (KS), characterized by transient skin blistering followed by abnormal pigmentation, skin atrophy, and skin cancer, is caused by mutations in the FERMT1 gene. Although a few KS patients have been reported to also develop ulcerative colitis (UC), a causal link to the FERMT1 gene mutation is unknown. The FERMT1 gene product belongs to a family of focal adhesion proteins (Kindlin-1, -2, -3) that bind several β integrin cytoplasmic domains. Here, we show that deleting Kindlin-1 in mice gives rise to skin atrophy and an intestinal epithelial dysfunction with similarities to human UC. This intestinal dysfunction results in perinatal lethality and is triggered by defective intestinal epithelial cell integrin activation, leading to detachment of this barrier followed by a destructive inflammatory response.

Mutations in FERMT1, coding for the Kindlin-1 protein, cause Kindler Syndrome in humans, characterized by skin blistering, atrophy, and cancer. Recent reports showed that some Kindler Syndrome patients additionally suffer from ulcerative colitis. However, it is unknown whether this is caused by loss of Kindlin-1 or by unrelated abnormalities such as infections or additional mutations. We ablated the Fermt1 gene in mice to directly analyze the pathological consequences and the molecular mode of action of Kindlin-1. Kindlin-1–deficient mice develop a severe epidermal atrophy, but lack blisters. All mutant mice die shortly after birth from a dramatic, shear force-induced detachment of intestinal epithelial cells followed by a profound inflammation and organ destruction. The intestinal phenotype is very similar to, although more severe than, the one observed in Kindler Syndrome patients. In vitro studies revealed that impaired integrin activation, and thus impaired adhesion, to the extracellular matrix of the intestinal wall causes intestinal epithelial cell detachment. Therefore, we demonstrate that intestinal epithelial cells require adhesive function of integrins to resist the shear force applied by the stool. Furthermore, we provide evidence that the colitis associated with Kindler Syndrome is caused by a dysfunction of Kindlin-1 rather than by a Kindlin-1–independent event.

Obesity resistance of the stearoyl-CoA desaturase-deficient (scd1-/-) mouse results from disruption of the epidermal lipid barrier and adaptive thermoregulation

Targeted deletion of the stearoyl-CoA desaturase 1 gene (scd1) in mouse causes obesity resistance and a severe skin phenotype. Here, we demonstrate that SCD1 deficiency disrupts the epidermal lipid barrier and leads to uncontrolled transepidermal water loss, breakdown of adaptive thermoregulation and cold resistance, as well as a metabolic wasting syndrome. The loss of omega-hydroxylated very long-chain fatty acids (VLCFA) and ceramides substituted with omega-hydroxylated VLCFA covalently linked to corneocyte surface proteins leads to the disruption of the epidermal lipid barrier in scd1-/- mutants. Artificial occlusion of the skin by topical lipid application largely reconstituted the epidermal barrier and also reversed dysregulation of thermogenesis and cold resistance, as well as the metabolic disturbances. Interestingly, SCD1 deficiency abolished expression of the key transcription factor Lef1, which is essential for interfollicular epidermis, sebaceous glands, and hair follicle development. Finally, the occurrence of SCD1 and a newly described hSCD5 (ACOD4) gene in humans suggests that the scd1-/- mouse mutant might be a valuable animal model for the study of human skin diseases associated with epidermal barrier defects.

An overview of cutaneous mosaicism

Cutaneous mosaicism is a poorly understood but relatively common dermatological finding. This paper reviews basic concepts of mosaicism as well as common and rare mosaic skin disorders.

Xeroderma pigmentosum, trichothiodystrophy and Cockayne syndrome: a complex genotype-phenotype relationship

Patients with the rare genetic disorders, xeroderma pigmentosum (XP), trichothiodystrophy (TTD) and Cockayne syndrome (CS) have defects in DNA nucleotide excision repair (NER). The NER pathway involves at least 28 genes. Three NER genes are also part of the basal transcription factor, TFIIH. Mutations in 11 NER genes have been associated with clinical diseases with at least eight overlapping phenotypes. The clinical features of these patients have some similarities but also have marked differences. NER is involved in protection against sunlight-induced DNA damage. While XP patients have 1000-fold increase in susceptibility to skin cancer, TTD and CS patients have normal skin cancer risk. Several of the genes involved in NER also affect somatic growth and development. Some patients have short stature and immature sexual development. TTD patients have sulfur deficient brittle hair. Progressive sensorineural deafness is an early feature of XP and CS. Many of these clinical diseases are associated with developmental delay and progressive neurological degeneration. The main neuropathology of XP is a primary neuronal degeneration. In contrast, CS and TTD patients have reduced myelination of the brain. These complex neurological abnormalities are not related to sunlight exposure but may be caused by developmental defects as well as faulty repair of DNA damage to neuronal cells induced by oxidative metabolism or other endogenous processes.

Cancer-associated genodermatoses: a personal history

Cancer-associated genodermatoses are a group of genetic disorders inherited in an autosomal-dominant fashion in which unique cutaneous findings are a reliable marker for the risk of developing internal malignancies. The historical, clinical and dermatopathological aspects of basal cell nevus syndrome, Muir-Torre syndrome, Cowden syndrome, Carney complex and Birt-Hogg-Dubé syndrome are reviewed in a personal and informal fashion. The latest advances in the molecular genetics of the disorders are also summarized.

The alpha-3 polypeptide chain of laminin 5: insight into wound healing responses from the study of genodermatoses

Laminin 5 (kalinin/epiligrin/nicein) is an essential structural component of the dermal-epidermal junction, composed of three polypeptide subunits: laminin alpha3, beta3 and gamma2. Studies of the inherited skin fragility disorder junctional epidermolysis bullosa (JEB) have suggested that the major role of this heterotrimeric protein is to act as an adhesive ligand essential for binding the epidermis to the underlying dermis and thus maintaining the integrity of the skin. Protein interaction studies have shown that the C terminus of the alpha3 subunit binds to a range of integrin complexes depending on the motility status of keratinocytes. This allows laminin 5 to interact with either hemidesmosomes or the actin cytoskeleton. Recently we have reported that the absence of the N-terminal region of laminin alpha3a in laryngo-onchyo-cutaneous syndrome causes excessive granulation tissue production at wound sites. As granulation tissue production is also a problem in JEB, this implicates laminin 5 in control of this wound healing response.

Gap junction diseases of the skin

Gap junctions are intercellular channels that allow the passage of water, ions, and small molecules. They are involved in quick, short-range messaging between cells and are found in skin, nervous tissue, heart, and muscle. An increasing number of hereditary skin disorders appear to be caused by mutations in one of the genes coding for the constituent proteins of gap junctions, known as connexins. In this review, the currently known connexin disorders that feature skin abnormalities are described: keratitis-ichthyosis deafness syndrome, erythrokeratoderma variabilis, Vohwinkel's syndrome, and a novel disorder called hypotrichosis-deafness syndrome. What is known about the pathogenesis of these disorders is discussed and related to gap junction physiology.

Association of cervical artery dissection with connective tissue abnormalities in skin and arteries

Spontaneous cervical artery dissections (sCAD) often occur in otherwise healthy individuals without known risk factors for stroke and frequently develop spontaneously without relevant trauma. An underlying arteriopathy leading to a so-called 'weakness of the vessel wall' and predisposing certain individuals to dissection has often been postulated. Therefore, the morphology of connective tissue, a main component of vessel wall and environment, was investigated in carotids and skin. While the overall morphology of dermal connective tissue is normal, about half of patients with sCAD show mild ultrastructural connective tissue alterations. These ultrastructural morphological aberrations can be designated either as 'Ehlers-Danlos syndrome (EDS) III-like', resembling mild findings in patients with the hypermobility type of EDS (EDS III); or coined 'EDS IV-like' with collagen fibers containing fibrils with highly variable diameters resembling mild findings in vascular EDS; or the abnormalities are restricted to the elastic fibers (with fragmentation and minicalcifications) without significant alterations in the morphology of the collagen fibrils. These findings had some similarity with the morphology found in heterozygous carriers of pseudoxanthoma elasticum. A grading scale according to the severity of the findings has been introduced. Similar connective tissue abnormalities were detected in some first-degree relatives of patients with sCAD showing hereditary at least in a subgroup. They can serve as a phenotypic marker for further genetic studies in patients with sCAD and large families to possibly identify the underlying basic molecular defect(s). Very few of patients (<5%) with sCAD and connective tissue abnormalities have clinical manifestations of skin, joint, or skeletal abnormalities of a defined heritable connective tissue disorder. In specimens of arterial walls of carotid, aortic, and renal arteries of patients with sCAD, pronounced systemic, histopathological, and ultrastructural abnormalities were detected with elastic fiber fragmentation and medial degeneration, described before only in a few patients with known hereditary connective tissue diseases such as the Marfan syndrome. We hypothesize that a major part of sCAD cases represents a manifestation of a connective tissue disorder with a vascular phenotype.

The quest for the function of simple epithelial keratins

Simple epithelial keratins K8 and K18 are components of the intracellular cytoskeleton in the cells of the single-layered sheet tissues inside the body. As members of the intermediate filament family of proteins, their function has been a matter for debate since they were first discovered. Whilst there is an indisputable case for a structural cell-reinforcing function for keratins in the mutilayered squamous epithelia of external barrier tissues, some very different stress-protective features now seem to be emerging for the simple epithelial keratins. Even the emerging evidence of pathological mutations in K8/K18 looks very different from mutations in stratified epithelial keratins. K8/K18-like keratins were probably the first to evolve and, whilst stratified epithelial (keratinocyte) keratins have diversified into a large group of keratins highly specialised for providing mechanical stability, the simple epithelial keratins have retained early features that may protect the internal epithelia from a broader range of stresses, including osmotic stress and chemical toxicity.

Divergent effects of two sequence variants of GJB3 (G12D and R32W) on the function of connexin 31 in vitro

Recently, we identified several missense mutations of the connexin gene GJB3 encoding connexin 31 (Cx31) in erythrokeratodermia variabilis (EKV), an autosomal dominant skin disorder. These mutations include G12D, which replaces a conserved glycine residue in the amino-terminus of Cx31 and is associated with a severe EKV phenotype. In contrast, the biologic relevance of the GJB3 sequence variant R32W located in the first transmembrane domain of Cx31 is disputed. To examine the effects of these sequence variants on Cx31 biogenesis and gap junction activity we expressed wild type and mutant Cx31-Flag constructs in HeLa cells. Using immunostaining, all expression variants were detected in the cytoplasm and in a punctate pattern at the cell surface, indicating that G12D and R32W did not interfere with either protein synthesis or transport to the cell membrane. Similarly, oligomerization into hemichannels appeared not impaired when expressing either Cx31 mutant as assessed by size exclusion chromatography, immunoblotting and immunostaining. However, dye transfer experiments and monitoring of intracellular calcium levels in response to serum stimulation revealed that G12D-Cx31 did not form functional gap junction channels, probably due to incorrect assembly or altered properties of Cx31 channels. In contrast, intercellular coupling between cells expressing R32W-Cx31 was comparable to that of wtCx31, suggesting that R32W is a functionally inconsequential polymorphism of Cx31.

Darier disease with paired segmental manifestation of either excessive or absent involvement: a further step in the concept of twin spotting

For the first time, we describe a case of type 2 segmental Darier disease with concomitant band-like areas of healthy skin. This clinical observation gives a further hint for the understanding of type 2 segmental manifestations in autosomal dominant diseases. We had observed a 17-year-old patient with Darier disease since the age of 13 years. On the frontal aspect of his body, the lesions were found to be diffusely and rather symmetrically disseminated. On the back, however, a band-like pattern of pronounced involvement with concomitant streaks of healthy skin, both following the lines of Blaschko, was noted. Type 2 segmental manifestation of autosomal dominant disorders can be explained by the assumption that the individual carries a germline mutation that gives rise to a diffuse, nonsegmental distribution of the disease. In addition, a postzygotic mutation occurring at an early developmental stage would result in loss of heterozygosity and give rise, in a segmental area, to a homozygous or hemizygous state of the mutation. This would explain the enhanced severity of the segmental lesions. Theoretically, an early event of mitotic recombination should give rise, simultaneously, to a clone of cells that are homozygous for the corresponding wild-type allele, and for this reason paired segmental areas of either excessive or absent involvement, in the form of twin spotting, should occur on the background of an ordinary, nonsegmental phenotype, as exemplified by Happle and König in a case of epidermolytic hyperkeratosis of Brocq. These authors stated that, in autosomal dominant skin disorders, segmental areas of healthy skin will usually be difficult to recognize. This may explain why such a twin spot phenomenon has so far not been encountered in Darier disease.

Late recurrence of inflammatory first-stage lesions in incontinentia pigmenti: an unusual phenomenon and a fascinating pathologic mechanism

BACKGROUND

Incontinentia pigmenti (IP) is an X-linked genodermatosis that is manifested by neonatal inflammatory vesicles localized along the lines of Blaschko. These lesions usually clear spontaneously within a few months, leaving hyperpigmentation. Ophthalmologic and neurologic symptoms can be associated with IP. Late recurrences of the first-stage inflammatory lesions after the initial rash are uncommon and have been reported infrequently. The mechanism involved in this phenomenon is unclear. However, the recent identification of NEMO/IKKgamma as the gene responsible for IP sheds new light on its pathophysiologic origins.

OBSERVATIONS

We report 5 cases of children who experienced episodes of late reactivation of IP. In all cases, the recurrences occurred on the previously hyperpigmented streaks several months or years after resolution of the initial eruptions. In most cases, the recurrences were preceded by an infectious episode.

CONCLUSIONS

These IP recurrences suggest that mutated cells can persist a long time in the epidermis. We theorize that infections trigger the reactivations. The NEMO/IKKgamma gene encodes a protein essential in nuclear factor kappaB activation, which is required for resistance to tumor necrosis factor alpha-induced apoptosis. We discuss the role of a proinflammatory cytokine such as tumor necrosis factor alpha as a triggering factor for the reactivation.

Dohi Memorial Lecture. New aspects of cutaneous mosaicism

The concept of cutaneous mosaicism has today been proven at the cellular level in at least fifteen different skin disorders. We can distinguish five different patterns of mosaicism, including the phylloid pattern and the lateralization pattern. Etiologically, cutaneous mosaics can be divided into two large categories, epigenetic mosaicism and genomic mosaicism. All forms of epigenetic mosaicism known so far, including the various patterns of X-inactivation, appear to be caused by the action of retrotransposons. A new concept is functional autosomal mosaicism transmittable through the action of retrotransposons, which has been described in mice and dogs and may explain, for example, the familial occurrence of pigmentary mosaicism along the Blaschko lines in human skin. Among the examples of mosaicism of autosomal lethal mutations, phylloid hypomelanosis is a recently recognized neurocutaneous entity caused by mosaic trisomy 13. Possible examples of a type 2 segmental manifestation now include at least fifteen different autosomally dominant skin disorders. This phenomenon is most frequently found in glomangiomatosis, cutaneous leiomyomatosis, and disseminated superficial actinic porokeratosis. Recently proposed examples of didymosis (twin spotting) include cutis tricolor, paired patches of excessive or absent involvement in Darier disease, and didymosis aplasticosebacea characterized by coexistent aplasia cutis congenita and nevus sebaceus. To the list of possible examples of paradominant inheritance, cutis marmorata telangiectatica congenita and speckled lentiginous nevus syndrome have now been added. Revertant mosaicism giving rise to unaffected skin areas in autosomally recessive cutaneous traits will certainly likewise be recognized more often when clinicians are bearing this concept in mind. Such cases can be taken as examples of "natural gene therapy".

Beauty is skin deep: the fascinating biology of the epidermis and its appendages

A number of fascinating questions remain unaddressed in the realm of skin biology. We still know very little about the mechanisms that set up the patterning of hair follicles over the surface ectoderm, or about the precise signalling pathways involved in mesenchymal-epithelial interactions during hair development and differentiation. Studies over the past 10 years have implicated both the notch and sonic hedgehog pathways in these processes (Chen et al., 1997; Chiang et al., 1999; Crowe et al., 1998; Kopan and Weintraub, 1993; Nohno et al., 1995; Oro and Scott, 1998; Powell et al., 1998; St. Jacques et al., 1998). Furthermore, we know that members of the fibroblast growth factor and bone morphogenic protein families are also involved in mesenchymal-epithelial cues required for follicle morphogenesis, hair cycling, and/or follicle differentiation (Hebert et al., 1994; Jung et al., 1998; Kratochwil et al., 1996; Noramly and Morgan, 1998; Rosenquist and Martin, 1996; Song et al., 1996). However, it is not clear precisely how these pathways and factors are involved and how they might also interact with the wnt pathway in regulating hair follicle patterning and morphogenesis. These areas are currently centers of activity in the field, and answers will undoubtedly emerge with the flurry of new experiments presently being conducted. Another important issue is the residence of stem cells within the skin. While it is clear that the epidermis contains a population of cells with extraordinary proliferative capacity (Jones and Watt, 1993; Jones et al., 1995), their precise location in most body regions of the skin remains unclear. Similarly, while the bulge hypothesis has received considerable attention and support as the residence of the hair follicle stem cells (Cotsarelis et al., 1989; Lavker et al., 1993), the outer root sheath and the matrix of the follicle have also been postulated as potential homes for these critical cells (Oliver and Jahoda, 1988; Rochat et al., 1994). An equally challenging issue for the future is the extent to which skin stem cells might retain pluripotency, able to choose between an epidermal or hair follicle cell fate. Our recent studies implicating a Wnt pathway provide a starting point for exploration. I have discussed a number of recent insights that have surfaced concerning transcriptional regulation in the epidermis. Additionally, besides Lef1/beta-catenin, there are a number of transcription factors that have been identified that are likely to regulate key aspects of hair follicle differentiation and gene expression. The most interesting of these include a member, Whn, of the winged-helix transcription factors, recently been shown to be the defect underlying the nude mouse phenotype (Nehls et al., 1994; Segre et al., 1995) and the zinc finger transcription factor responsible for the hairless phenotype in mice and in humans (Ahmad et al., 1998; Cachon-Gonzalez et al., 1994). A major area for future study will be to elucidate the upstream and/or downstream targets of Lef1/beta-catenin, hairless, and whn. Let me close by returning to the issues of structure and function in the skin and to the underlying genetic basis of skin disorders. It is surprising that despite nearly 20 years of molecular genetics and its application to skin biology, we still know very little about the molecules and pathways involved in the acquisition of the epidermal barrier, the very purpose of the epidermis. Biochemical studies have given us clues as to the most important lipids involved (for review, see Proksch et al., 1993), and recent studies suggest that barrier function may in part be regulated through action of the steroid hormone superfamily of receptors (Attar et al., 1997; Hardman et al., 1998). A major research effort is now needed to begin to decipher the transcriptional regulation and the complex pathways involved in lipid synthesis and packaging. (ABSTRACT TRUNCATED)

[Keratin diseases]

The rapid development in human genome research has resulted in a tremendous increase in our understanding of the molecular basis of many genetic skin diseases. One outstanding example of this is diseases caused by mutations in keratin genes, which comprise several disorders of the epidermis, as for example the different types of epidermolysis bullosa simplex. In this respect, the most important questions have been to 1. Define the molecular defect. 2. Unravel the pathophysiological mechanisms that lead to the characteristic phenotype and 3. Design of new therapeutic strategies. Molecular research has contributed significantly to the first two issues whereas a therapeutic break-through has yet to appear.