Exclusion of linkage between the collagenase gene and generalized recessive dystrophic epidermolysis bullosa phenotype

Molecular-based phenotype variations in amelogenesis imperfecta

Amelogenesis imperfecta (AI) is one of the typical dental genetic diseases in human. It can occur isolatedly or as part of a syndrome. Previous reports have mainly clarified the types and mechanisms of nonsyndromic AI. This review aimed to compare the phenotypic differences among the hereditary enamel defects with or without syndromes and their underlying pathogenic genes. We searched the articles in PubMed with different strategies or keywords including but not limited to amelogenesis imperfecta, enamel defects, hypoplastic/hypomaturation/hypocalcified, syndrome, or specific syndrome name. The articles with detailed clinical information about the enamel and other phenotypes and clear genetic background were used for the analysis. We totally summarized and compared enamel phenotypes of 18 nonsyndromic AI with 17 causative genes and 19 syndromic AI with 26 causative genes. According to the clinical features, radiographic or ultrastructural changes in enamel, the enamel defects were basically divided into hypoplastic and hypomineralized (hypomaturated and hypocalcified) and presented a higher heterogeneity which were closely related to the involved pathogenic genes, types of mutation, hereditary pattern, X chromosome inactivation, incomplete penetrance, and other mechanisms.The gene-specific enamel phenotypes could be an important indicator for diagnosing nonsyndromic and syndromic AI.

A frequent functional SNP in the MMP1 promoter is associated with higher disease severity in recessive dystrophic epidermolysis bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is caused by mutations in the COL7A1 gene encoding type VII collagen. Variations in severity between the different clinical forms of RDEB likely depend on the nature and location of COL7A1 mutations, but observed intrafamilial phenotypic variations suggest additional genetic and/or environmental factors. Candidate modifier genes include MMP1, encoding matrix metalloproteinase 1, the first gene implicated in RDEB before its primary role in the disease was excluded. Type VII collagen is a substrate of MMP1 and an imbalance between its synthesis and degradation could conceivably worsen the RDEB phenotype. Here, we studied a previously described family with three affected siblings of identical COL7A1 genotype but displaying great sibling-to-sibling variations in disease severity. RDEB severity did not correlate with type VII collagen synthesis levels, but with protein levels at the dermal-epidermal junction, suggesting increased degradation by metalloproteinases. This was supported by the presence of increased transcript and active MMP1 levels in the most severely affected children, who carried a known SNP (1G/2G) in the MMP1 promoter. This SNP creates a functional Ets binding site resulting in transcriptional upregulation. We next studied a French cohort of 31 unrelated RDEB patients harboring at least one in-frame COL7A1 mutation, ranging from mild localized RDEB to the severe Hallopeau-Siemens form. We found a strong genetic association between the 2G variant and the Hallopeau-Siemens disease type (odds ratio: 73.6). This is the first example of a modifier gene in RDEB and has implications for its prognosis and possible new treatments.

Using Urgotul dressing for the management of epidermolysis bullosa skin lesions

OBJECTIVE

To evaluate the acceptability, tolerance and efficacy of Urgotul wound dressing in the management of epidermolysis bullosa (EB) skin lesions.

METHOD

This was an open-label uncontrolled clinical trial involving 20 patients (I I adults and nine children) with EB simplex or dystrophic EB. Patients were selected from the register of EB patients at the investigating centre and included if they presented with at least one skin lesion requiring management with a non-adherent wound dressing. Lesions were treated with the study dressing for a maximum of four weeks. All dressing changes, wound parameters, pain and effect on quality of life were recorded.

RESULTS

All patients completed the trial. Nineteen out of 20 wounds healed within 8.7 +/- 8.5 days. Overall, 11 patients (55%) considered that their quality of life had improved following use of the dressing, which was also reported to be pain free and 'very easy' or 'easy' to remove at most dressing changes. Nineteen out of 20 patients stated that they would use the study dressing to manage their lesions in future.

CONCLUSION

This study confirmed the very good acceptability and efficacy of Urgotul in the treatment of skin lesions in patients with EB.

Skin expression of metalloproteinases and tissue inhibitor of metalloproteinases in sibling patients with recessive dystrophic epidermolysis and intrafamilial phenotypic variation

A number of COL7A1 mutations have now been reported in recessive dystrophic epidermolysis bullosa patients, and the analysis of phenotype-genotype correlations showed evidence for interfamilial and intrafamilial phenotypic variability, occurring for the same mutation. Collagenase and stromelysin activities have been found to be overexpressed in skin cultures of some recessive dystrophic epidermolysis bullosa patients, and tissue destruction in the disease process might result from an imbalance of metalloproteinases (MMP) over tissueinhibitor of metalloproteinases (TIMP). So we suspected that the phenotypic variability for the same mutation could be linked to other genetic or environmental factors, as a particular balance between MMP and TIMP. Organ cultures were performed using explants from the skin of three patients from the same family with recessive dystrophic epidermolysis bullosa to reveal and quantify the expression of MMP-1 (collagenase 1), MMP-2 and MMP-9 (gelatinases A and B), MMP-3 (stromelysin 1), TIMP-1, and TIMP-2, and to compare the results with those obtained with two human control skins, with the same experimental conditions. Increased amounts of all metalloproteinases investigated were observed in the skin of the three recessive dystrophic epidermolysis bullosa affected sibling brothers, both in lesioned and in apparently nonlesioned skin, compared with controls. The amounts of MMP-1, MMP-2, MMP-3, and MMP-9 increased particularly in the skin of the more clinically affected patient. Furthermore for this patient we evidenced higher amounts of MMP-1 and also a lower TIMP-1 amount in his unlesioned and lesioned skin compared with the other two affected patients and with healthy control donors. So we can suspect that recessive dystrophic epidermolysis bullosa phenotypic variability could be related to patients' collagenase activity heterogeneity, linked to imbalance between MMP-1 and TIMP-1.

Recent advances in the molecular basis of inherited skin diseases

Over the last few years the molecular basis of several inherited skin diseases has been delineated. Some discoveries have stemmed from a candidate gene approach using clinical, biochemical, immunohistochemical, and ultrastructural clues, while others have arisen from genetic linkage and positional cloning analyses. Notable advances have included elucidation of specific gene pathology in the major forms of inherited skin fragility, ichthyosis, and keratoderma. These findings have led to a better understanding of the significance of individual structural proteins and regulatory enzymes in keratinocyte adhesion and differentiation. From a clinical perspective, the advances have led to better genetic counseling in many disorders, the development of DNA-based prenatal diagnosis, and a foundation for planning newer forms of treatment, including somatic gene therapy, in selected conditions.

Investigation of the relationship between osteoporosis and the collagenase gene by means of polymorphism of the 5'upstream region of this gene

Osteoporosis is a slowly progressing disease resulting from an imbalance between bone accretion and degradation. As interstitial collagenase is a key enzyme in the degradation of bone matrix, we investigated a possible relationship between the collagenase gene and osteoporosis. Analysis of an amplified genomic DNA fragment from -524 to +52 by denaturing gradient gel electrophoresis and sequencing allowed us to detect three dimorphic sites upstream of base -300, one of them leading to a BanI restriction site. None of the sites could be directly associated with osteoporosis. The allele frequencies of the three dimorphic sites were estimated. The interallelic ratios were high, thus providing new useful genetic markers for linkage analysis. When comparing these ratios in osteoporotic and nonosteoporotic subjects, no significant differences could be observed.

Molecular basis for the dystrophic forms of epidermolysis bullosa: mutations in the type VII collagen gene

Significant progress has recently been made in understanding the molecular basis of heritable skin diseases, such as epidermolysis bullosa, a group of mechano-bullous genodermatoses. In particular, the dystrophic forms of epidermolysis bullosa have been shown to result from distinct mutations in the gene encoding type VII collagen, the major, if not the exclusive, component of the anchoring fibrils. These mutations result in deficient synthesis and/or altered assembly of the anchoring fibrils, thus compromising the integrity of the cutaneous basement membrane zone. The mutations in the type VII collagen gene have implications for understanding the structure-function relationships of the type VII collagen molecule, and also provide the basis for prenatal DNA-based diagnosis in families at risk for recurrence of the disease. Finally, understanding the genetic basis of dystrophic forms of EB sets the stage for gene therapy approaches for the treatment of these devastating skin diseases.

Epidermolysis bullosa: hereditary skin fragility diseases as paradigms in cell biology

Recent research into the molecular basis of epidermolysis bullosa has provided a unique insight into a variety of mechanisms in normal cell biology, such as cell-matrix interactions, and has uncovered an excellent model for studies on keratin intermediate filaments. The simplex forms of epidermolysis bullosa are caused by mutations in the genes for the basal epidermal keratins, K5 and K14. Most mutations affect highly conserved parts of the molecules, illustrating their importance in normal keratin filament assembly and integrity. Mutations in corresponding regions of the differentiation-associated keratins, K1 and K10 can also occur in epidermolytic ichthyosis. Both recessive and dominant forms of dystrophic epidermolysis bullosa result from mutations in an anchoring fibril collagen gene, COL7A1. Junctional epidermolysis bullosa is caused by mutations in the genes encoding different chains of the novel laminin isoform, nicein/kalinin, also known as laminin 5, which is associated with the anchoring filament-hemidesmosome complex of the basement membrane zone. These recent findings strengthen the evidence for the role of nicein/kalinin and type VII collagen in adherence and stabilization of the dermo-epidermal junction.

Genetic linkage to the type VII collagen gene (COL7A1) in 26 families with generalised recessive dystrophic epidermolysis bullosa and anchoring fibril abnormalities

To strengthen the evidence for genetic linkage to COL7A1, we have studied 26 generalised recessive dystrophic epidermolysis bullosa (EB) families of British, Italian, Irish, and South African origin. We chose two linkage markers, a COL7A1 PvuII intragenic polymorphism and a highly informative anonymous microsatellite marker, D3S1100, which maps close to the COL7A1 locus at 3p21.1-3. Diagnosis was established by family history, clinical examination, immunofluorescence, and ultrastructural studies. The PvuII marker was informative in 16 families with a maximum lod score (Zmax) of 3.51 at recombination fraction (theta) = 0. The D3S1100 microsatellite was informative in 24 out of 25 families with Zmax = 6.8 at theta = 0.05 (Z = 4.94 at theta = 0) and no obligatory recombination events. These data strongly suggest that COL7A1 mutations cause EB in these families and, combined with previous studies, indicate locus homogeneity. The importance of anchoring fibrils for dermal-epidermal adhesion is further underlined. D3S1100 may later prove useful in prenatal diagnosis of this disease, if used in combination with other markers.

Mutation detection by denaturing gradient gel electrophoresis (DGGE)

The molecular analysis of genetic diseases relies on several technical approaches which allow genetic and physical mapping, characterization of the gene structure, expression studies, and identification of disease-causing mutations. Denaturing gradient gel electrophoresis (DGGE) allows the rapid screening for single base changes in enzymatically amplified DNA. The technique is based on the migration of double-stranded DNA molecules through polyacrylamide gels containing linearly increasing concentrations of a denaturing agent. In this review DGGE and the several modifications of the original protocol are presented. Moreover, its applications in human molecular genetics are summarized together with a preliminary comparison with other mutation detection technologies such as chemical cleavage, RNase protection, and single-strand conformation polymorphism.

Gene expression of collagenase and stromelysin in skin fibroblasts derived from dystrophic epidermolysis bullosa

We studied expression of collagenase gene and stromelysin gene in skin fibroblasts derived from patients with recessive dystrophic epidermolysis bullosa (RDEB) and dominant dystrophic epidermolysis bullosa (DDEB). Northern blot analyses revealed that collagenase gene expression was markedly increased in two of four RDEB cells, as compared with three normal control cells. Moreover, stromelysin gene expression was also markedly increased in two RDEB cells, as compared with normal controls. In contrast, collagenase and stromelysin gene expression levels in three DDEB cells did not show any significant difference from those of normal controls, except one cell line which showed mild increase of both collagenase and stromelysin mRNA. Quantitative estimates of collagenase mRNA (U/micrograms RNA) determined by slot blot hybridizations showed that those of RDEBs: 0.92-1.81 (mean 1.3 +/- 0.45); DDEBs: 0.18-0.73 (mean 0.60 +/- 0.37); normal controls: 0.26-0.93 (mean 0.64 +/- 0.34). Stromelysin mRNA levels showed that those of RDEBs: 1.75-6.62 (mean 4.06 +/- 2.00); DDEBs: 0.55-3.78 (mean 1.69 +/- 1.81); normal controls: 1.27-2.08 (mean; 1.55 +/- 0.45). These data demonstrated that collagenase and stromelysin gene expression was increased in some, but not all, RDEB cell lines. Our data suggested that collagenase and/or stromelysin could play a certain role for blister formation in RDEB, coordinately or in a distinct manner.

Genetic linkage of recessive dystrophic epidermolysis bullosa to the type VII collagen gene

Generalized mutilating recessive dystrophic epidermolysis bullosa (RDEB) is characterized by extreme skin fragility owing to loss of dermal-epidermal adherence. Immunohistochemical studies have implicated type VII collagen, the major component of anchoring fibrils, in the etiology of RDEB. In this study, we demonstrate genetic linkage of the type VII collagen gene and the generalized mutilating RDEB phenotype. We first identified a Pvull polymorphic site by digestion of an amplified product of the type VII collagen gene, which was shown to reside within the coding region. Genetic linkage analysis between this marker and the RDEB phenotype in 19 affected families which were informative for this polymorphism showed no recombination events, and gave a maximum lod score of 3.97 at a recombination fraction (theta) of 0, demonstrating that this DNA region is involved in this form of RDEB. These data provide strong evidence that the type VII collagen gene, which has also been linked with the dominant form of the disease, harbors the mutation(s) causing the generalized mutilating form of RDEB in these families, thus underscoring the major functional importance of type VII collagen in basement membrane zone stability.

Genetic linkage of type VII collagen (COL7A1) to dominant dystrophic epidermolysis bullosa in families with abnormal anchoring fibrils

Epidermolysis bullosa (EB) in a group of genodermatoses characterized by the fragility of skin. Previous studies on the dystrophic (scarring) forms of EB have suggested abnormalities in anchoring fibrils, morphologically recognizable attachment structures that provide stability to the association of the cutaneous basement membrane to the underlying dermis. Since type VII collagen is the major component of the anchoring fibrils, we examined the genetic linkage of dominant dystrophic EB (EBDD) and the type VII collagen gene (COL7A1) locus, which we have recently mapped to chromosome 3p, in three large kindreds with abnormal anchoring fibrils. Strong genetic linkage of EBDD and COL7A1 loci was demonstrated with the maximum logarithm of odds (LOD) score of 8.77 at theta = 0. This linkage was further confirmed with two additional markers in this region of the short arm of chromosome 3, and these analyses allowed further refinement of the map locus of COL7A1. Since there were no recombinants between the COL7A1 and EBDD loci, our findings suggest that type VII collagen is the candidate gene that may harbor the mutations responsible for the EB phenotype in these three families.

Molecular biology and pathology of type VII collagen*

Type VII collagen is a genetically distinct member of the collagen family of proteins. Type VII collagen has been shown to be the major component of anchoring fibrils, attachment complexes which secure the cutaneous basement membrane of the skin to the underlying dermis. Understanding of the structure of type VII collagen has been advanced by recent cloning of the corresponding gene. Chromosomal mapping of the gene to the short arm of chromosome 3 and identification of intragenic polymorphic markers have allowed demonstration of strong genetic linkage between the type VII collagen locus and the dystrophic forms of EB (epidermolysis bullosa). This overview summarizes the progress made in the molecular genetics of type VII collagen.