180-kDa bullous pemphigoid antigen defective generalized atrophic benign epidermolysis bullosa: report of four cases with an unusually mild phenotype

Junctional epidermolysis bullosa: genotype-phenotype correlations

Junctional epidermolysis bullosa most commonly results from mutations in theLAMA3, LAMB3, LAMC2, COL17A1, ITGA6 and ITGB4genes. Junctional epidermolysis bullosa is characterized by clinical heterogeneity. To date, scientific findings allow to evaluate correlations between the severity of clinical manifestations and genetic defects underlying in the development of the disease. A systematic literature search was performed using PubMed and RSCI, and keywords including junctional epidermolysis bullosa, laminin 332, collagen XVII, 64 integrin. The review includes description of clinical findings of junctional epidermolysis bullosa, mutation location and types, its impact on protein production and functions. To evaluate the impact of gene mutation on protein functions, this review explores the structure and functions of lamina lucida components, including laminin 332, collagen XVII and 64 integrin, which are frequently associated with the development of junctional epidermolysis bullosa. The correlation between severe types of junctional epidermolysis bullosa and mutations resulting in premature stop codon generation and complete absence of protein expression has been described. Although, genotype-phenotype correlations should be analyzed carefully due to mechanisms which enable to improve protein expression.

Junctional epidermolysis bullosa of late onset explained by mutations in COL17A1

BACKGROUND

  Junctional epidermolysis bullosa of late onset (JEB-lo) is a rare disease characterized by blistering of primarily the hands and feet starting in childhood. The pathogenesis remains unclear.

OBJECTIVES

To clarify the pathogenesis of JEB-lo.

METHODS

Two patients with JEB-lo, a brother and a sister, were examined using electron microscopy (EM), immunofluorescence (IF) antigen mapping and molecular analysis.

RESULTS

We found subtle changes in IF antigen mapping and EM. The most remarkable changes were loss of the apical-lateral staining of monoclonal antibodies (mAbs) against type XVII collagen (Col17), and a broadened distribution of mAb staining against the ectodomain of Col17, laminin-332 and type VII collagen. Mutation analysis of COL17A1, encoding Col17, showed a compound heterozygosity for a novel mutation c.1992_1995delGGGT and the known mutation c.3908G>A in both patients. The deletion c.1992_1995delGGGT results in a premature termination codon and mRNA decay, leaving the patients functionally hemizygous for the missense mutation c.3908G>A (p.R1303Q) in the noncollagenous 4 domain of Col17.

CONCLUSIONS

JEB-lo is an autosomal recessive disorder caused by mutations in COL17A1, and subtle aberrations in EM and IF antigen mapping are clues to diagnosis.

Localized and generalized forms of blistering in junctional epidermolysis bullosa due to COL17A1 mutations in the Netherlands

BACKGROUND

Mutations in the gene COL17A1 coding for type XVII collagen cause non-Herlitz junctional epidermolysis bullosa (nH-JEB).

OBJECTIVES

Here we give an overview of the genotype-phenotype correlation in 12 patients from the Netherlands with type XVII collagen-deficient nH-JEB.

PATIENT AND METHODS

Family and personal history and clinical presentation were recorded from each patient, and skin biopsies of intact and bullous skin were taken for immunofluorescence and electron microscopy. The mutations were identified by analysing the patient's DNA isolated from peripheral blood cells.

RESULTS

DNA analysis identified five novel deletions: 1284delA, 1365delC, 3236delT, 3600-3601delCT and 4425delT. Interestingly, we identified a new patient, homozygous for 4425delT, with an exceptionally mild blistering phenotype. All together, three patients had more localized blistering confined to hands, lower legs and face, absent or very mild nail dystrophy, normal primary hair and sparse secondary hair. Nine patients had generalized blistering, nail dystrophy, sparse primary and absent secondary hair. All 12 patients had amelogenesis imperfecta (enamel pitting). Immunofluorescence (IF) antigen mapping with monoclonal antibodies 1A8C and 1D1 that bind to type XVII collagen, but not to its 97-kDa fragment was completely negative in patients with generalized blistering, whereas reduced in patients with localized blistering.

CONCLUSIONS

Our data reveal that in patients with COL17A1 mutations a localized nH-JEB phenotype can be differentiated from a generalized nH-JEB phenotype by IF antigen mapping. The data are important for genetic counselling at early age when the clinical phenotype is not yet clear.

Inherited junctional epidermolysis bullosa in the German Pointer: establishment of a large animal model

Junctional epidermolysis bullosa (JEB) is a genodermatosis suitable for gene therapy because conventional treatments are ineffective. Here, we elucidate the genetic basis of mild JEB in a breed of dogs that display all the clinical traits observed in JEB patients. The condition is associated with reduced expression of laminin 5 caused by a homozygous insertion (4818+207ins6.5 kb) of repetitive satellite DNA within intron 35 of the gene (lama3) for the laminin alpha3 chain. The intronic mutation interferes with maturation of the alpha3 pre-messenger RNA resulting in the coexpression of a transcript with a 227 nucleotide insertion and a wild-type mRNA that encodes scant amounts of the alpha3 polypeptide. Our results show that the amino acid sequence and structure of the canine and human alpha3 chain are highly conserved and that the reduced expression of laminin 5 affects the adhesion and clonogenic potential of the JEB keratinocytes. These JEB dogs provide the opportunity to perform gene delivery in a naturally occurring genodermatosis and to evaluate host tolerance to recombinant laminin 5.

A founder COL17A1 splice site mutation leading to generalized atrophic benign epidermolysis bullosa in an extended inbred Palestinian family from Israel

PURPOSE

Generalized atrophic benign epidermolysis bullosa is a nonlethal form of junctional EB with an autosomal recessive inheritance. There is generalized cutaneous blister formation at sites of trauma, atrophic alopecia affecting scalp, eyelash and eyebrow, dystrophic nail changes, and tooth abnormalities. In this study, we have studied a five-generation Palestinian family affected with generalized atrophic benign epidermolysis bullosa.

METHODS

We have performed linkage analysis to genes that are mutated in generalized atrophic benign epidermolysis bullosa, followed by direct sequencing of patient genomic DNA.

RESULTS

We have shown that the disease is caused by a newly detected homozygous donor splice site mutation, IVS51+1G>A, in the type XVII collagen gene, COL17A1.

CONCLUSION

The effect of a founder mutation introduced 3 to 4 generations before a disease appearance is demonstrated in this inbred family.

Type XVII collagen gene mutations in junctional epidermolysis bullosa and prospects for gene therapy

Non-Herlitz junctional epidermolysis bullosa (nH-JEB) is caused predominantly by mutations leading to premature stop codons on both alleles of the type XVII collagen gene (COL17A1). The analysis of mutations in this gene has provided a means of correlating genotype with phenotype of nH-JEB patients. The phenotype of nH-JEB is characterized by generalized blistering of skin and mucous membranes with atrophic scarring and nail dystrophy. Atrophic alopecia is a distinct feature of nH-JEB patients, but one that is not associated with the severity of the disease at other sites. Enamel hypoplasia and pitting of the teeth are also characteristic for nH-JEB and can be used to facilitate the correct diagnosis in children with a blistering skin disease. Analysis of the biological consequences of mutations in the COL17A1 gene has shown that most patients lack type XVII collagen mRNA due to nonsense-mediated mRNA decay. Patients with these mutations can therefore be a target for corrective gene therapy using vectors coding for full-length type XVII collagen. Proof of principle for this approach has recently been demonstrated. The analysis of naturally occurring phenomena of gene correction in the COL17A1 gene provides evidence for other mechanisms of gene correction in genetic diseases. For example, exclusion of an exon carrying a mutation can lead to a milder phenotype of nH-JEB than predicted by the original mutation. In addition, we have gained data suggesting that COL17A1 exons harbouring pathogenic mutations can also be repaired by trans-splicing, i.e. aligning corrected RNA sequences to introns in the vicinity of faulty exons in the COL17A1 premtRNA.

Truncated typeXVII collagen expression in a patient with non-herlitz junctional epidermolysis bullosa caused by a homozygous splice-site mutation

SUMMARY

Type XVII collagen (180-kDa bullous pemphigoid antigen) is a structural component of hemidesmosomes. Mutations in the type XVII collagen gene (COL17A1) have been established to be the molecular basis of non-Herlitz junctional epidermolysis bullosa (JEB-nH), an inherited skin blistering disorder. Here we report for the first time truncated type XVII collagen expression, caused by homozygosity for a COL17A1 donor splice-site mutation (4261+1 g --> c), which was identified by PCR amplification on genomic DNA. By RT-PCR and sequencing of cDNA derived from mRNA from the patient's cultured keratinocytes, we provide evidence of cryptic splicing and exon skipping, most abundantly of exon 52. JEB-nH patients with COL17A1 splice-site mutations resulting in an exon skip often have no immunologically detectable type XVII collagen. However, in our patient with the generalized atrophic benign epidermolysis bullosa subtype, a small amount of type XVII collagen was detectable in the skin, and immunoblotting of cultured keratinocytes revealed that the 180-kDa protein was 10 kDa shorter. We hypothesize that the function of this truncated type XVII collagen polypeptide, which is expressed at low levels, is impaired, explaining the JEB-nH phenotype.

A homozygous nonsense mutation in type XVII collagen gene (COL17A1) uncovers an alternatively spliced mRNA accounting for an unusually mild form of non-Herlitz junctional epidermolysis bullosa

In this study we describe six Italian patients presenting an unusually mild variant of non-Herlitz junctional epidermolysis bullosa associated with a reduced expression of type XVII collagen. All patients are homozygous for a novel nonsense mutation (R795X) within exon 33 of COL17A1 and show a common haplotype, attesting propagation of an ancestral allele within the Italian population. Analysis of patients' COL17A1 transcripts showed the presence of two mRNA species: a normal-sized mRNA carrying mutation R795X that undergoes rapid decay, and a transcript generated by in-frame skipping of exon 33. Patients keratinocytes were shown to synthesize minute amounts of type XVII collagen, which appeared correctly localized along the cutaneous basement membrane. We therefore suggest that the exon 33-deleted COL17A1 splice variant encodes for type XVII collagen molecules that maintain a functional role and account for the mild phenotype of our patients.

Hemizygosity for a glycine substitution in collagen XVII: unfolding and degradation of the ectodomain

Defects of collagen XVII, a keratinocyte adhesion protein, are associated with epidermal detachment in junctional epidermolysis bullosa. Although some missense mutations in the collagen XVII gene COL17A1 have been described, the molecular mechanisms leading to disease have remained elusive in these cases. Here we assessed the biologic consequences of a missense mutation by studying the folding and stability of wild-type and mutated recombinant collagen XVII domains. The mutation occurred in a junctional epidermolysis bullosa patient who was compound heterozygous for the novel glycine substitution mutation G633D and the novel nonsense mutation R145X. Collagen XVII mRNA was significantly reduced, indicating nonsense-mediated mRNA degradation and hemizygosity of the patient for the G633D substitution. As glycine residues within the collagen triple helices are important for stable conformation, the thermal stability of the wild-type and mutated eukaryotic recombinant Col15 domain of collagen XVII was assessed. The stability of the mutated fragment was clearly reduced. The midpoint of the helix-to-coil transition, Tm, was 5 degrees C lower than that of wild-type rCol15, indicating abnormal triple-helix folding and susceptibility to proteolysis. Consistently, immunoassays demonstrated reduced amounts of the full-length collagen XVII and absence of the soluble ectodomain in keratinocyte cultures, and lack of the ectodomain from the junctional epidermolysis bullosa skin. These observations show that the glycine substitution G633D in collagen XVII causes abnormal folding and susceptibility to degradation, and thus perturbs the physiologic adhesive functions of collagen XVII in the skin.

Hereditary skin diseases of hemidesmosomes

Studies of hereditary blistering skin diseases (epidermolysis bullosa) and targeted gene mutation experiments in knockout mice have greatly improved our understanding of hemidesmosomes and their associated structures in the cytoskeleton and basement membrane of the skin and mucous membranes. At least 10 molecules are recruited in hemidesmosome complexes, where they interact in a complex way. Hemidesmosomes are not simple adhesion devices, but also transduce signals for cell spreading, cell proliferation and basement membrane organisation. The dynamics of a hemidesmosome raises the metaphor of a self-assembling suspension bridge which evokes activities on both sides of the river. This review summarises our current knowledge of the molecular pathology of hemidesmosomes caused by hereditary skin disease or gene targeting experiment.