Linkage studies in erythrokeratodermias: fine mapping, genetic heterogeneity and analysis of candidate genes

Atrial Fibrillation: Focus on Myocardial Connexins and Gap Junctions

Atrial fibrillation (AF) represents the most common type of clinical cardiac arrhythmia worldwide and contributes to substantial morbidity, mortality and socioeconomic burden. Aggregating evidence highlights the strong genetic basis of AF. In addition to chromosomal abnormalities, pathogenic mutations in over 50 genes have been causally linked to AF, of which the majority encode ion channels, cardiac structural proteins, transcription factors and gap junction channels. In the heart, gap junctions comprised of connexins (Cxs) form intercellular pathways responsible for electrical coupling and rapid coordinated action potential propagation between adjacent cardiomyocytes. Among the 21 isoforms of connexins already identified in the mammal genomes, 5 isoforms (Cx37, Cx40, Cx43, Cx45 and Cx46) are expressed in human heart. Abnormal electrical coupling between cardiomyocytes caused by structural remodeling of gap junction channels (alterations in connexin distribution and protein levels) has been associated with enhanced susceptibility to AF and recent studies have revealed multiple causative mutations or polymorphisms in 4 isoforms of connexins predisposing to AF. In this review, an overview of the genetics of AF is made, with a focus on the roles of mutant myocardial connexins and gap junctions in the pathogenesis of AF, to underscore the hypothesis that cardiac connexins are a major molecular target in the management of AF.

Relationship between SNP rs1764391 and Susceptibility, Risk Factors, Gene-environment Interactions of Acute Myocardial Infarction in Guangxi Han Chinese Population

BACKGROUND

Large-scale population studies showed that the SNP rs1764391 of Connexin37 gene also known as Cx37 gene may play a pivotal role in the occurrence and development of acute myocardial infarction (AMI). Published results, however, are highly controversial.

OBJECTIVE

This study aimed to examine the association between SNP rs1764391 of Cx37 and diseasesusceptibility, several risk factors, and gene-environment interactions of AMI in Guangxi Han Chinese population.

METHODS

In this study, 344 healthy controls and 344 AMI patients of Han Chinese population were enrolled. The TaqMan assay was implemented to identify genotypes of Cx37 and allele frequencies of SNP rs1764391 in both the AMI and control groups.

RESULTS

Significant differences were detected in TT genotype frequencies of SNP rs1764391 between the AMI and control groups (P < 0.05). In the context of gender stratification, the result was also statistically different in women (P < 0.05). Each variable such as age, BMI, diabetes, high blood pressure, smoking and TC was a risk factor and correlated significantly (P < 0.05) with the development of AMI. HDL-C correlated negatively with the risk of AMI (P < 0.001). BMI, smoking or alcohol consumed interacts significantly (P < 0.017) with the presence of the SNP rs1764391 CC genotype.

CONCLUSION

Evidences were presented that Cx37 rs1764391 variation may contribute to the risk for AMI, especially in women and this genetic variant may prove to be a potential biomarker for AMI risk stratification and may prove to be a useful target for therapeutic intervention to further improve prognosis in high-risk patients.

Mutations in cardiovascular connexin genes

Connexins (Cxs) form a family of transmembrane proteins comprising 21 members in humans. Cxs differ in their expression patterns, biophysical properties and ability to combine into homomeric or heteromeric gap junction channels between neighbouring cells. The permeation of ions and small metabolites through gap junction channels or hemichannels confers a crucial role to these proteins in intercellular communication and in maintaining tissue homeostasis. Among others, Cx37, Cx40, Cx43, Cx45 and Cx47 are found in heart, blood and lymphatic vessels. Mutations or polymorphisms in the genes coding for these Cxs have not only been implicated in cardiovascular pathologies but also in a variety of other disorders. While mutations in Cx43 are mostly linked to oculodentodigital dysplasia, Cx47 mutations are associated with Pelizaeus-Merzbacher-like disease and lymphoedema. Cx40 mutations are principally linked to atrial fibrillation. Mutations in Cx37 have not yet been described, but polymorphisms in the Cx37 gene have been implicated in the development of arterial disease. This review addresses current knowledge on gene mutations in cardiovascular Cxs systematically and links them to alterations in channel properties and disease.

[Erythrokeratodermia variabilis]

BACKGROUND

Erythrokeratodermia variabilis (EKV) is a rare genodermatosis associated with keratinisation disorders. Mutations are found in genes encoding connexin 31 and 30.3 mapped to chromosome 1 p34-35. We report two cases of EKV, one of which presented dramatic improvement with oral retinoids.

PATIENTS AND METHODS

A 15-month-old boy was referred to us with reddish-brown hyperkeratotic and well-demarcated plaques on the extremities, axillary space and face. The lesions started when he was 6months of age. Cutaneous histopathology showed acanthosis and papillomatosis associated with orthokeratotic hyperkeratosis. Anatomoclinical comparison confirmed the diagnosis of EKV. A second child aged 10years was referred to us with fixed, well-demarcated hyperkeratotic plaques associated with transient red patches. The lesions began when she was 1month old. Anatomoclinical comparison confirmed the diagnosis of EKV and the patient showed dramatic improvement after 2weeks on acitretin.

DISCUSSION

EKV is characterized by the association of fixed well-demarcated plaques and transient erythematous patches. Although cutaneous histopathology is not specific, a typical physical examination and a compatible cutaneous histopathology can aid the diagnosis. Oral retinoids are often very rapidly effective.

Progressive symmetric erythrokeratodermia with delayed intellectual milestones and convulsions

Progressive symmetric erythrokeratoderma is an uncommon genodermatosis and is thought to arise due to mutations in the connexin gene, however, genetic heterogenicity has been described. Very few cases of neurological involvement have been described in this unusual entity. We report a case of progressive symmetric erythrokeratoderma, with convulsions and delayed intellectual milestones.

Digenic inheritance of non-syndromic deafness caused by mutations at the gap junction proteins Cx26 and Cx31

Mutations in the genes coding for connexin 26 (Cx26) and connexin 31 (Cx31) cause non-syndromic deafness. Here, we provide evidence that mutations at these two connexin genes can interact to cause hearing loss in digenic heterozygotes in humans. We have screened 108 GJB2 heterozygous Chinese patients for mutations in GJB3 by sequencing. We have excluded the possibility that mutations in exon 1 of GJB2 and the deletion of GJB6 are the second mutant allele in these Chinese heterozygous probands. Two different GJB3 mutations (N166S and A194T) occurring in compound heterozygosity with the 235delC and 299delAT of GJB2 were identified in three unrelated families (235delC/N166S, 235delC/A194T and 299delAT/A194T). Neither of these mutations in Cx31 was detected in DNA from 200 unrelated Chinese controls. Direct physical interaction of Cx26 with Cx31 is supported by data showing that Cx26 and Cx31 have overlapping expression patterns in the cochlea. In addition, by coimmunoprecipitation of mouse cochlear membrane proteins, we identified the presence of heteromeric Cx26/Cx31 connexons. Furthermore, by cotransfection of mCherry-tagged Cx26 and GFP-tagged Cx31 in human embryonic kidney (HEK)-293 cells, we demonstrated that the two connexins were able to co-assemble in vitro in the same junction plaque. Together, our data indicate that a genetic interaction between these two connexin genes can lead to hearing loss.

Production of anti-epithelial antibodies and acantholysis by vaccination with an anti-idiotypic antibody, mimicking desmoglein 1

Theoretically, the immunization of experimental animals with an anti-idiotype antibody may elicit antibodies that recognize epitopes like the original idiotype; this is archived via internal images. Using this strategy, we attempted to produce anti-epithelial antibodies in Balb/c mice immunized with a pemphigus anti-idiotypic determinant. First, when an anti-idiotype antibody was produced in rabbits by immunization with pemphigus immunoglobulin G (IgG), the anti-idiotypic activity was tested successfully. The anti-idiotype IgG was digested with pepsin and purified by gel filtration chromatography to obtain F(ab')(2) fragments, which were used to immunize Balb/c mice. A control group was immunized with normal IgG. The experimental animals immunized with anti-idiotype F(ab')(2) fragments developed anti-epithelial antibodies in the following two months. The elicited antibodies had anti-desmoglein 1 specificity. Additionally, the skin biopsies of these animals exhibited antibody deposition along intercellular spaces of epidermis, and 25% of them developed blisters. Sera and skin biopsies of control Balb/c mice group were negative. In conclusion, the immunization with pemphigus anti-idiotype antibody may elicit anti-epithelial antibodies via internal images. This experimental approach can be used to understand the pathogenic mechanisms of pemphigus.

Connexin37: a potential modifier gene of inflammatory disease

There is an increasing appreciation of the importance of gap junction proteins (connexins) in modulating the severity of inflammatory diseases. Multiple epidemiological gene association studies have detected a link between a single nucleotide polymorphism in the human connexin37 (Cx37) gene and coronary artery disease or myocardial infarction in various populations. This C1019T polymorphism causes a proline-to-serine substitution (P319S) in the regulatory C terminal tail of Cx37, a protein that is expressed in the vascular endothelium as well as in monocytes and macrophages. Indeed, these three cell types are key players in atherogenesis. In the early phases of atherosclerosis, blood monocytes are recruited to the sites of injury in response to chemotactic factors. Monocytes adhere to the dysfunctional endothelium and transmigrate across endothelial cells to penetrate the arterial intima. In the intima, monocytes proliferate, mature, and accumulate lipids to progress into macrophage foam cells. This review focuses on Cx37 and its impact on the cellular and molecular events underlying tissue function, with particular emphasis of the contribution of the C1019T polymorphism in atherosclerosis. We will also discuss evidence for a potential mechanism by which allelic variants of Cx37 are differentially predictive of increased risk for inflammatory diseases.

Clinical and Genetic Heterogeneity of Erythrokeratoderma Variabilis

The skin disease erythrokeratoderma variabilis (EKV) has been shown to be associated with mutations in GJB3 and GJB4 encoding connexin (Cx)31 and Cx30.3, respectively. Gap junctions composed of Cx proteins are intracellular channels providing a mechanism of synchronized cellular response facilitating metabolic and electronic functions of the cell. In the skin, Cx31 and Cx30.3 are expressed in the stratum granulosum of the epidermis with a suggested role in late keratinocyte differentiation. Molecular investigations of GJB3 and GJB4 were performed in five pedigrees and three sporadic cases of EKV. Mutational analyzes revealed disease-associated Cx31 or Cx30.3 mutations in only three probands of which two were novel mutations and one was a recurrent mutation. These genetic studies further demonstrate the heterogeneous nature of the erythrokeratodermas as not all individuals that were clinically diagnosed with EKV harbor Cx31 or Cx30.3 mutations.

Erythrokeratodermas: A classification in a state of flux?

The term 'erythrokeratodermas' or 'erythrokeratodermias' has been applied to a group of inherited disorders characterized by well-demarcated erythematous lesions and hyperkeratotic plaques. Connexin mutations have been demonstrated to be responsible for most cases of erythrokeratoderma variabilis but there remain some cases without demonstrated connexin mutations, suggesting genetic heterogeneity. The position of progressive symmetric erythrokeratoderma has become rather unclear. Loricin mutations have been found in some cases that clinically resemble variant Vohwinkel syndrome and other cases have features that overlap with those of erythrokeratoderma variablis. Whether progressive symmetric erythrokeratoderma exists as a distinct entity is under question.

Association between C1019T polymorphism of connexin37 and acute myocardial infarction: a study in patients from Sicily

During atherogenesis, a critical role is played by intercellular communication via gap junctions, cell membrane channels linking the cytoplasmic compartments of adjacent cells. The component protein subunits of these channels, called connexin (Cx), belong to a multigene family. Cx37 is involved in growth, regeneration after injury and ageing of the endothelial cells, suggesting its role in atherosclerosis. The C1019 single nucleotide polymorphism (SNP) of Cx37 gene was associated with thickening of the carotid intima in Swedish men and was also associated with coronary artery disease in a Taiwanese population. On the other hand, in two more recent studies performed in male Japanese population, T1019 Cx37 SNP has shown to be a risk factor for acute myocardial infarction (AMI). In the light of these discrepant results, we have studied the frequency of this SNP in a very homogeneous cohort of young male people affected by AMI. We analysed 97 male Sicilian patients (mean age 40, age range 20-46) and 196 healthy male controls (mean age 39, age range 20-55) for C1019T of the Cx37. The 1019T SNP was significantly increased in the patients compared to the controls (43.8% vs. 34.4%; p=0.03 by chi2 test with Yates' correction; odds ratio (OR) 1.5, (1.0-2.1) 95% confidence interval (CI)). The present case control study performed in a homogeneous Caucasoid population confirms the Japanese results that T SNP of Cx37 gene is involved in AMI phenotype, demonstrating the consistency of the association across past studies and across different populations. The differences between patients and controls are significant but relatively small with an odd ratio risk of 1.5. However, as AMI is a multifactorial disease, any single mutation will only provide a small or modest contribution to risk, also depending on interaction with other genes and/or a particular environment.

A new, recurrent mutation of GJB3 (Cx31) in erythrokeratodermia variabilis

BACKGROUND

Erythrokeratodermia variabilis (EKV) is an autosomal dominant or recessive genodermatosis characterized by the coexistence of randomly occurring, transient, erythematous patches and hyperkeratosis of the skin. The disorder has been mapped to chromosome 1p35.1 but is genetically heterogeneous. EKV may be caused by pathogenic mutations in one of two neighbouring connexin genes, GJB3 and GJB4, encoding the gap junction proteins Cx31 and Cx30.3, respectively. Twelve distinct mutations identified to date cluster either at the cytoplasmic amino-terminus or in the four transmembrane domains.

OBJECTIVES

To report a large family with EKV and an unrelated sporadic case.

METHODS

DNA amplification and mutation analysis, followed by denaturing high-performance liquid chromatography to confirm the segregation of the mutations in the two families with EKV.

RESULTS

A novel, recurrent GJB3 mutation (625C-->T; L209F) was identified in the family with EKV and in the unrelated sporadic case.

CONCLUSIONS

This mutation is the first to affect a conserved residue in the cytoplasmic carboxy-terminus of any connexin gene with a cutaneous phenotype, emphasizing its structural and/or functional importance.

Cx31 andCx43 double-deficient mice reveal independent functions in murine placental and skin development

The overlapping expression of gap junctional connexins in tissues has indicated that the channels may compensate for each other. During development, Cx31 and Cx43 are coexpressed in preimplantation embryos, in the spongiotrophoblast of the placenta and in the epidermis. This study shows that Cx31/Cx43 double-deficient mice exhibit the known phenotypes of the single-knockout strains but no combined effects. Thus, Cx43, coexpressed with Cx31 at midgestation in the spongiotrophoblast of the placenta, cannot be responsible for a partial rescue of the lethal Cx31 knockout phenotype, as assumed before (Plum et al. [2001] Dev Biol 231:334-337). It follows that both connexins have unique functions in placental development. Despite an altered expression of other epidermal connexin mRNAs, epidermal differentiation and physiology was unaltered by the absence of Cx31 and Cx43. Therefore, in epidermal and preimplantation development, gap junctional communication can probably be compensated by other isoforms coexpressed with Cx31 and Cx43.

Connexin disorders of the skin

Over the past decade, the molecular basis of most disorders of cornification has been unveiled. Among these, a distinct group has emerged because of primary defects in cell-cell communication due to faulty gap junction proteins also known as connexins. This review aims to delineate the cutaneous connexin disorders and to highlight intriguing genotype-phenotype correlations and emanating clinical implications.

Case study: erythrokeratodermia variabilis

A 4-year-old girl presented to the dermatology clinic with complaints of erythematous skin lesions on her face, extremities,forearms, and joints. The patient was a product of a full-term, normal pregnancy and delivery and was born to healthy parents. The parents are cousins. The condition started a few months after birth with small, hyperkeratotic patches on her cheeks. These lesions did not respond to the treatment that was given. The condition progressed and a few months later similar skin lesions started to appear on her forearms and knees. Different types of treatment, such as topical antibiotics,emollients, topical steroids, and systemic antihistamines, have been tried without any benefit. Some lesions showed variable exacerbations and remissions. There was no family history of a similar problem, although her older brother showed marginal hair loss without any skin lesions. On physical examination (Figures 1-3), hyperkeratotic erythrodermic plaques of variable thickness with sharply demarcated borders were seen on cheeks, extensor surfaces of forearms, and on the knees. The palms,soles, nails, and teeth were normal. The hair showed normal appearance, but there was no hair growth on the margins of the scalp. The laboratory investigations showed normal complete blood count and normal serum zinc and ferritin levels. Urine microscopy and examination was normal. Skin biopsy was taken and histopathology showed nonspecific features of hyperkeratosis with moderate papillomatosis and acanthosis (Figure 4). A diagnosis of erythrokeratodermia variabilis was made and the patient was started on emollients as treatment. There was not much improvement with the treatment.

The role of connexins in human disease

Connexins are the building blocks of gap junctions. In forming a gap junction, six connexins oligomerize to form a hexameric torus called a connexon. The number of gap junctions in a cell ranges from a few to over 105 and imparts to interconnected cells a uniform phenotype. The crucial role that gap junctions play in normal physiology is reflected by the diverse spectrum of human diseases in which allele variants of different gap junction genes are implicated. In particular, mutations in GJB2 are a major cause of autosomal recessive non-syndromic deafness. This discovery has impacted medical practice and makes it incumbent on clinicians to familiarize themselves with the genetic advances that are rapidly occurring in our field.

Ichthyosis: etiology, diagnosis, and management

The ichthyoses are a heterogeneous group of disorders with both inherited and acquired forms. Clinical presentation, pattern of inheritance, and laboratory evaluation may establish a precise diagnosis, which can assist in prognosis and genetic counseling. Congenital autosomal recessive ichthyosis (CARI) usually presents at birth, often as a collodion baby. CARI can progress into any one of a spectrum of disorders. Lamellar ichthyosis is characterized by dark, plate (armor)-like scale. This disease is often caused by mutations in the gene encoding the enzyme transglutaminase 1. Congenital ichthyosiform erythroderma is another phenotype within CARI, marked by generalized redness and fine white scale. Epidermolytic hyperkeratosis is an autosomal dominant disorder characterized by hyperkeratosis and blistering, and at least six clinical phenotypes have been described. It may be due to mutations in the gene encoding the intermediate filament proteins keratin 1 and 10. Ichthyosis vulgaris is the most common ichthyosis, and is inherited in an autosomal dominant pattern. Involvement is generally mild and may vary greatly with climate and humidity. X-linked ichthyosis, due to a defect in the enzyme steroid sulfatase, affects males with generalized scaling that usually begins soon after birth. There may be associated corneal opacities that do not affect vision. Sjögren-Larsson syndrome is an autosomal recessive ichthyosis associated with progressive spastic paralysis and mental retardation. This condition is caused by mutations in the gene for fatty aldehyde dehydrogenase. Refsum's disease, due to accumulation of phytanic acid, results in ichthyosis and progressive neurologic dysfunction. The erythrokeratodermas are characterized by hyperkeratosis and localized erythema. Erythrokeratodermia variabilis is autosomal dominant and characterized by generalized or localized hyperkeratosis and migratory red patches. Mutations in the genes encoding the gap junction proteins, connexins, underlie this disorder. Netherton's syndrome is an autosomal recessive disorder characterized by ichthyosis, a hair shaft abnormality and atopy. The ichthyosis may present at birth with erythroderma or in some cases a collodion presentation. However, a frequent characteristic skin manifestation is ichthyosis linearis circumflexa. Netherton's syndrome has been found to be due to an abnormality in a serum protease inhibitor. Acquired ichthyosis can have a variety of underlying causes including neoplastic, infectious, drugs, endocrine, metabolic, autoimmune, malabsorptive states, and hereditary. Topical, and in more severe cases, systemic, therapy are useful in managing this array of disorders of cornification.

Genetic heterogeneity in erythrokeratodermia variabilis: novel mutations in the connexin gene GJB4 (Cx30.3) and genotype-phenotype correlations

Erythrokeratodermia variabilis is an autosomal dominant genodermatosis characterized by persistent plaque-like or generalized hyperkeratosis and transient red patches of variable size, shape, and location. The disorder maps to a cluster of connexin genes on chromosome 1p34-p35.1 and, in a subset of families, results from mutations in the gene GJB3 encoding the gap junction protein connexin-31 (Cx31). A recent report suggested the involvement of another connexin gene (GJB4) in the etiology of erythrokeratodermia variabilis. In this study, we sequenced the coding region of GJB4 in 13 unrelated erythrokeratodermia variabilis families without detectable mutations in GJB3. Mutation analysis revealed six distinct missense mutations in five families and a sporadic case of erythrokeratodermia variabilis, all of which were not found in controls. Mutation G12D, identified in an extended Dutch family, lies in the predicted amino-terminus and may interfere with the flexibility of this domain, connexin selectivity, or gating polarity of gap junction channels. Other mutations (R22H, T85P, F137L, F189Y) were located in the transmembrane domains of Cx30.3, and are predicted to hinder regulation of voltage gating or alter the kinetics of channel closure. Affected individuals of two unrelated families harbored point mutations leading to amino acid substitution F137L, which was also reported in GJB3, yet the extent and severity of hyperkeratosis was milder compared to the corresponding mutation in GJB3. Two mutations (T85P, F137L) were associated with the occurrence of rapidly changing erythematous patches with prominent, circinate, or gyrate borders in affected children but not in adults, supporting the notion that this feature is specific to Cx30.3 defects. Nevertheless, we observed highly variable intrafamilial phenotypes, suggesting the strong influence of modifying genetic and epigenetic factors. In addition to pathogenic mutations, we identified several missense mutations and a 4 bp deletion within the GJB4 coding region, which might represent either inconsequential polymorphisms or recessive mutations. In conclusion, our results demonstrate genetic heterogeneity in erythrokeratodermia variabilis, and emphasize that intercellular communication mediated by both Cx31 and Cx30.3 is crucial for epidermal differentiation.

Prediction of the risk of myocardial infarction from polymorphisms in candidate genes

BACKGROUND

Although epidemiologic studies have suggested that several genetic variants increase the risk of myocardial infarction, large-scale association studies that examine many polymorphisms simultaneously are required to allow reliable prediction of the genetic risk of myocardial infarction.

METHODS

We used a fluorescence- or colorimetry-based allele-specific DNA-primer-probe assay system to determine the genotypes of 112 polymorphisms of 71 candidate genes in 2819 unrelated Japanese patients with myocardial infarction (2003 men and 816 women) and 2242 unrelated Japanese controls (1306 men and 936 women).

RESULTS

In an initial screening of the 112 polymorphisms for an association with myocardial infarction in 909 subjects, 19 polymorphisms were selected in men and 18 in women by means of logistic-regression analysis, after adjustment for age, body-mass index, and the prevalence of smoking, hypertension, diabetes mellitus, hypercholesterolemia, and hyperuricemia. In a large-scale study involving the selected polymorphisms and the remaining 4152 subjects, similar logistic-regression analysis revealed that the risk of myocardial infarction was significantly associated with the C1019T polymorphism in the connexin 37 gene (P<0.001) in men and the 4G-668/5G polymorphism in the plasminogen-activator inhibitor type 1 gene (P<0.001) and the 5A-1171/6A polymorphism in the stromelysin-1 gene (P<0.001) in women.

CONCLUSIONS

Determination of the genotypes of the connexin 37, plasminogen-activator inhibitor type 1, and stromelysin-1 genes may prove reliable in predicting the genetic risk of myocardial infarction and might thus contribute to the primary prevention of this condition.

Erythrokeratodermia variabilis with erythema gyratum repens-like lesions

A large pedigree with erythrokeratodermia variabilis (EKV) and erythema gyratum repens-like lesions is described. Clinical, laboratory, and histologic findings of this family are presented. The differential diagnoses of the following dermatoses with an erythematous and a hyperkeratotic component are discussed: erythrokeratodermia variabilis (Mendes da Costa), progressive symmetric erythrokeratoderma (Gottron), loricrin keratoderma, erythrokeratoderma en cocardes (Degos), Netherton syndrome, keratitis-ichthyosis-deafness (KID) syndrome, erythrokeratolysis hiemalis (Oudtshoorn disease), and nonbullous congenital ichthyosiform erythroderma.

Connexin37 gene polymorphism and coronary artery disease in Taiwan

BACKGROUND

A recent study shows that a C1019T polymorphism of the gene encoding the gap junction protein connexin37 contributes to the genesis of atherosclerotic plaques in human carotid artery. However, whether such a polymorphism can be used as a prognostic marker in atherosclerotic disease of other arterial sites, such as coronary artery disease, is not known.

METHODS

We analyzed the allelic status in 177 subjects with coronary artery disease (age, 61+/-11 years; male/female, 120/57) and 102 controls (60+/-11 years; male/female, 70/32). Both groups were matched, before genotype analysis, for a variety of other traditional risk factors, including body mass index, smoking status, levels of blood pressure, sugar, creatinine, and lipid profiles, in addition to age and sex.

RESULTS

The T allele was less frequently seen in the control group, compared to the disease group (10.7 vs. 20.1%, TT+TC vs. CC, P<0.01). Subsequent analysis demonstrated that a significant difference existed in the male (9.2 vs. 22.8%, TT+TC vs. CC, P<0.005), but not in the female. Another finding was that the T allele frequency in all participants was less than 15%, markedly lower than that reported in non-Taiwanese.

CONCLUSIONS

The observation indicates that the polymorphism in the connexin37 gene potentially plays a role in the manifestation of coronary atherosclerosis in Taiwan.

Mutation in the gene for connexin 30.3 in a family with erythrokeratodermia variabilis

Erythrokeratodermia variabilis (EKV) is an autosomal dominant keratinization disorder characterized by migratory erythematous lesions and fixed keratotic plaques. All families with EKV show mapping to chromosome 1p34-p35, and mutations in the gene for connexin 31 (Cx31) have been reported in some but not all families. We studied eight affected and three healthy subjects in an Israeli family, of Kurdish origin, with EKV. After having mapped the disorder to chromosome 1p34-p35, we found no mutations in the genes for Cx31, Cx31.1, and Cx37. Further investigation revealed a heterozygous T-->C transition leading to the missense mutation (F137L) in the human gene for Cx30.3 that colocalizes on chromosome 1p34-p35. This nucleotide change cosegregated with the disease and was not found in 200 alleles from normal individuals. This mutation concerns a highly conserved phenylalanine, in the third transmembrane region of the Cx30.3 molecule, known to be implicated in the wall formation of the gap-junction pore. Our results show that mutations in the gene for Cx30.3 can be causally involved in EKV and point to genetic heterogeneity of this disorder. Furthermore, we suggest that our family presents a new type of EKV because of the hitherto unreported association with erythema gyratum repens.

Identification of a novel mutation R42P in the gap junction protein beta-3 associated with autosomal dominant erythrokeratoderma variabilis

We report a missense mutation in the gap junction protein beta-3 (encoding Connexin 31), which was detected in only the affected members of a family in which the autosomal dominant skin disease erythrokeratoderma variabilis was segregating. The nucleotide change results in an arginine to proline substitution in codon 42. This residue is positioned on the first transmembrane/first extracellular domain of the gap junction protein with the mutation replacing a negatively charged residue with a nonpolar residue. This change may disrupt the conformation of the protein and voltage gating polarity leading to impaired channel function.

A genetic polymorphism in connexin 37 as a prognostic marker for atherosclerotic plaque development

BACKGROUND AND OBJECTIVES

Atherosclerosis is a multifactorial disease, in part characterized by chronic inflammatory changes in the vessel wall and loss of normal physical and biochemical interactions between endothelial cells and smooth muscle cells. Previous studies [Hu J., Cotgreave IA. J Clin Invest; 99: 1-5] have provided molecular links between inflammation and myoendothelial communication via gap junctions, suggesting that these structures may be important in the development of the atherosclerotic vessel phenotype. In order to strengthen this premise, the aim of the present work was to probe for structural polymorphisms in connexin 37, a gap junctional protein uniquely expressed in endothelial cells, and to assess for potential genotypic segregation in individuals displaying atherosclerotic plaque.

METHODS AND RESULTS

Computer-based comparisons of Expressed Sequence Tags (ESTs) predicted a polymorphism in the human gap junctional protein connexin 37 (cx37). The C1019-T mutation results in a proline to serine shift at codon 319 (cx37*1-cx37*2). A Restriction Fragment Length Polymorphism (RFLP) assay, involving the insertion of a novel Drd I cleavage site in the proline variant revealed a statistically significant over-representation of the cx37*1 allele in association with atherosclerotic plaque-bearing individuals (Odds-ratio for the homozygote = 2.38, Chi2 = 7.693, P = 0.006), in comparison to individuals lacking plaque, irrespective of a history of hypertension.

CONCLUSIONS

These data suggest that the C1019-T polymorphism in cx37 may provide 'single gene marker', which could be useful in assessing atherosclerotic plaque development, particularly in cardiovascular risk groups such as those with borderline hypertension.

Inherited disorders of epidermal keratinization

There have been a number of major discoveries recently in the field of dermatological science which have enabled us to determine the causes of inherited skin diseases of previously unknown etiology. In this paper we will review some important aspects of the biology of epidermal differentiation and the recent advances in understanding of the molecular mechanism underlying genetic diseases of keratinization.

Mutations in the human connexin gene GJB3 cause erythrokeratodermia variabilis

Erythrokeratodermia variabilis (EKV, OMIM 133200) is an autosomal dominant genodermatosis with considerable intra- and interfamilial variability. It has a disfiguring phenotype characterized by the independent occurrence of two morphologic features: transient figurate red patches and localized or generalized hyperkeratosis. Both features can be triggered by external factors such as trauma to the skin. After initial linkage to the RH locus on 1p, EKV was mapped to an interval of 2.6 cM on 1p34-p35, and a candidate gene (GJA4) encoding the gap junction protein alpha-4 (connexin 31, Cx31) was excluded by sequence analysis. Evidence in mouse suggesting that the EKV region harbours a cluster of epidermally expressed connexin genes led us to characterize the human homologues of GJB3 (encoding Cx31) and GJB5 (encoding Cx31.1). GJB3, GJB5 and GJA4 were localized to a 1.1-Mb YAC in the candidate interval. We detected heterozygous missense mutations in GJB3 in four EKV families leading to substitution of a conserved glycine by charged residues (G12R and G12D), or change of a cysteine (C86S). These mutations are predicted to interfere with normal Cx31 structure and function, possibly due to a dominant inhibitory effect. Our results implicate Cx31 in the pathogenesis of EKV, and provide evidence that intercellular communication mediated by Cx31 is crucial for epidermal differentiation and response to external factors.