Absence of R42X and R635X mutations in the LAMB3 gene in 12 Japanese patients with junctional epidermolysis bullosa

A Japanese-specific recurrent mutation and a novel splice site mutation in the LAMC2 gene identified in two Japanese families with Herlitz junctional epidermolysis bullosa

BACKGROUND

Herlitz junctional epidermolysis bullosa (H-JEB) is an extremely rare genodermatosis characterized by lethality owing to severe blister formation. We report two unrelated Japanese patients with H-JEB. Genetic analyses detected a single nonsense mutation on the LAMC2 gene in these two patients.

AIM

To identify the mutation involved and describe the first reported Japanese recurrent mutation in the LAMC2 gene.

METHODS

Direct sequencing was performed of DNA from either peripheral blood or fetal cells in amniotic fluid. Reverse transcriptase PCR was used to confirm that an aberrant transcript resulted from the splice site mutation. A haplotype analysis was performed to define the origin of the recurrent mutation.

RESULTS

Both patients had blisters and erosions on the trunk and limbs at birth, with nail dystrophy. Patient 1 died as a result of sepsis at 30 weeks of age, and patient 2 died as a result of disseminated intravascular coagulation at 20 weeks of age. Mutation analysis of the LAMC2 gene revealed that patient 1 was compound heterozygous for a nonsense mutation (p.Cys553X) and a novel splice site mutation (c.2868+1delG), and patient 2 was a homozygous for p.Cys553X. Prenatal diagnosis performed during a subsequent pregnancy in family 2 revealed that this second child was heterozygous for p.Cys553X, and was thus not affected. Haplotype analysis suggested that a p.Cys553X allele derived from the same origin had been independently inherited by these two unrelated families.

CONCLUSIONS

p.Cys553X in the LAMC2 gene may be a Japanese-specific recurrent mutation as a result of a founder effect, and it may therefore be useful for initial screening in the mutation analysis of H-JEB.

Epidermolysis bullosa in Japan

Epidermolysis bullosa (EB) is a group of hereditary disorders characterized by mechanical stress-induced blistering of the skin and mucous membranes. This article discusses the prevalence among and genetic studies of Japanese patients with EB.

[Junctional epidermolysis bullosa. Identification of a new mutation in two Lebanese families]

BACKGROUND

Junctional epidermolysis bullosa (JEB) represents a genetically heterozygous group of bullous disorders characterized by dermo-epidermal separation resulting from mutations affecting the main dermo-epidermal adhesion factor, laminin-5, its cellular receptor, integrin alpha6B4, or collagen XVII. We report the identification of a new mutation of LAMA3, encoding laminin-5 alpha3 subunit in two unrelated Lebanese families.

PATIENTS AND METHODS

Two female newborn, descending from 1st degree consanguineous marriages, presented a lethal form of EBJ-Herlitz. Histologic, ultrastructural and immunofluorescence studies were performed in order to ascertain the diagnosis and to direct genetic analysis. Mutation search was conducted through direct DNA sequencing of patients and ascendants.

RESULTS

Immunohistology of frozen skin samples revealed an extremely reduced immunoreactivity for the alpha3 laminin-5 subunit. The two patients were homozygous carriers (parents heterozygous) of a new missense mutation of LAMA3 gene (exon 32: 4300 insA) encoding the alpha3 subunit of laminin-5. Resulting messenger RNA, rapidly degraded, induced an extremely reduced synthesis of alpha3-polypeptide, truncated in its Cterminal domain.

DISCUSSION

LAMB3 gene recurrent mutations R636X and R42X account for about 50p. 100 of EBJ cases affecting Caucasians while mutation Q1083X, affecting the same gene, is recurrent in Arab populations. The newly identified mutation results in extremely reduced synthesis of alpha3 chain and truncation of its C-terminal domain, which is crucial for the intermolecular interactions of laminin-5. Our data are in accordance with recent reports suggesting geographical specificity of EBJ mutations linked to founder effects which are amplified by consanguineous marriages in genetically isolated populations. Otherwise, the observation of other unexplored cases of bullous dermatoses with early demise originating from the same region of the two families herein reported highlights the need for the implementation of a prenatal and postnatal diagnostic strategy regarding these genodermatoses. These studies should target LAMA3 and other genes involved in JEB too.

Laminin-5 mutational analysis in an Italian cohort of patients with junctional epidermolysis bullosa

Junctional epidermolysis bullosa (JEB) is a rare genodermatosis characterized by dermal-epidermal separation that is caused by mutations in the genes encoding hemidesmosomal components and laminin-5, the major epithelial adhesion ligand. Here, we report on the mutational analysis of LAMA3, LAMB3, and LAMC2 genes encoding laminin-5 chains in 19 Italian patients, 11 affected with the severe Herlitz (H JEB) and eight with the mild non-Herlitz variant of JEB (non-H JEB). Eighteen mutations, seven of which were novel, were identified and their consequences analyzed at the mRNA and protein level. Premature termination codon mutations in both alleles of LAMB3 or LAMC2 genes were found in nine of the 11 H JEB patients, with a prevalence of mutations in LAMC2. In one case, a homozygous frameshift mutation in LAMB3 was associated to illegitimate splicing leading to non-H JEB. One H JEB patient showed a large intragenic duplication within LAMC2, a genetic defect so far uncovered in laminin-5 genes. Splicing or missense mutations, were prevalent in non-H JEB patients. Collectively, five mutations appeared to be frequent in laminin-5 JEB patients: R635X, 29insC, E210K, W143X in LAMB3 and R95X in LAMC2. These recurrent mutations account for approximately 44% of laminin-5 JEB alleles in Italian patients.

Animal models for skin blistering conditions: absence of laminin 5 causes hereditary junctional mechanobullous disease in the Belgian horse

Recent achievements in the genetic correction of keratinocytes isolated from patients with junctional epidermolysis bullosa have paved the way to a gene therapy approach for the disease. Because gene therapy protocols require preclinical validation in animals, we have characterized spontaneous animal models of junctional epidermolysis bullosa. In this study we have elucidated the genetic basis of the hereditary junctional mechanobullous disease in the Belgian horse, a condition characterized by blistering of the skin and mouth epithelia, and exungulation (loss of the hoof). Immunofluorescence analysis associated the condition to the absent expression of the gamma2 chain of laminin 5 and designated Lamc2 as the candidate gene. Comparative analysis of the nucleotide sequence of the full-length gamma2 cDNA isolated by reverse transcription polymerase chain reaction amplification of total RNA purified from the epithelium of a junctional epidermolysis bullosa foal and a healthy control disclosed a homozygous basepair insertion (1368insC) in the affected animal. Mutation 1368insC results in a downstream premature termination codon and is predicted to cause absent expression of the laminin gamma2 polypeptide. Our results also show that: (i) the horse junctional epidermolysis bullosa genetically corresponds to the severe Herlitz form of junctional epidermolysis bullosa in man; (ii) the amino acid sequence and structure of the horse laminin gamma2 chain are virtually identical to the human counterpart; (iii) the moderate eruption of skin blisters in the affected animals with respect to the human Herlitz junctional epidermolysis bullosa patients correlates with the protection provided by hair. Our observations suggest that the affected foals are a convenient source of epithelial cells from tissues that cannot be obtained from human junctional epidermolysis bullosa patients, and imply that hairless strains of animals with recessive skin disorders would be the best models for in vivo gene therapy approaches to skin blistering diseases.

Junctional epidermolysis bullosa in the Middle East: clinical and genetic studies in a series of consanguineous families

BACKGROUND

Junctional epidermolysis bullosa (JEB) is a group of inherited blistering diseases characterized by epidermal-dermal separation resulting from mutations that affect the function of critical components of the basement membrane zone. This group of autosomal recessive diseases is especially prevalent in regions where consanguinity is common, such as the Middle East. However, the clinical and genetic epidemiology of JEB in this region remains largely unexplored.

OBJECTIVE

The aim of the present study was to assess a series of consanguineous JEB families originating from the Middle East.

METHODS

We identified 7 families referred to us between 1998 and 1999 and originating from the United Arab Emirates, Saudi Arabia, Sudan, Yemen, and Israel. Histologic, immunofluorescence, and electron microscopy studies were performed to direct the subsequent molecular analysis. DNA obtained from all family members was amplified by means of polymerase chain reaction and analyzed by conformation-sensitive gel electrophoresis with subsequent direct sequencing.

RESULTS

In 6 families presenting with the clinical and histologic features distinctive for JEB, mutations in genes encoding 1 of the 3 subunit polypeptides of laminin-5 were identified. Two families each had mutations in LAMB3, 2 in LAMA3, and 2 in LAMC2. Out of 7 distinct mutations, 5 were novel and 2 were recurrent. No relationship was found between the presence of nonsense/frameshift mutations in laminin-5 genes and perinatal mortality, contradicting a major genotype-phenotype correlation previously reported in the European and US literature. Similarly, none of the recurrent LAMB3 hot spot mutations previously described in other populations was found in our series. Finally, in a family with the clinical diagnosis of generalized atrophic benign epidermolysis bullosa, a homozygous non-sense mutation in Col17A1 gene (encoding the BPAG2 antigen) was identified.

CONCLUSION

The present report suggests (1) the existence of a unique spectrum of mutations in the Middle East populations and (2) the need for the implementation of a diagnostic strategy tailored to the genetic features of JEB in this region.

Prenatal diagnosis as a test for genodermatoses: its past, present and future

The prenatal diagnosis (PND) of severe hereditary skin diseases started in the early 1980s using fetal skin biopsy techniques based on ultrastructural and immunohistochemical abnormalities of the fetal skin. Recent success in identifying responsible genes and demonstrating mutations in such genes has set the stage for DNA-based PND in the 1990s. Common examples of skin conditions which can be prenatally diagnosed include epidermolysis bullosa, oculocutaneous albinism and Harlequin ichthyosis in which the severity of the clinical phenotype appears to justify PND in families at risk. More recently, preimplantation diagnoses of inherited diseases have become possible using in vitro fertilization techniques. The diagnosis consists of a blastomere biopsy of the six to ten-cell embryo and a DNA analysis of single blastomeres. Disease-free embryos are selected for transfer to the uterus, thereby avoiding the need for termination of a fetus found to be affected by conventional PND. Furthermore, carrying out a PND using a single fetal cell from the maternal blood, such as nucleated erythrocytes, has become technically feasible. Although there are many questions that remain unanswered, the outlook for further development of noninvasive PND in the future appears optimistic.

Novel and de novo glycine substitution mutations in the type VII collagen gene (COL7A1) in dystrophic epidermolysis bullosa: implications for genetic counseling

The dystrophic forms of epidermolysis bullosa (DEB) are due to mutations in the type VII collagen gene (COL7A1). In dominant DEB, a characteristic genetic lesion is a glycine substitution mutation within the collagenous domain of the protein. In this study, we have examined the molecular basis of six new families in which the proband has clinical features and/or ultrastructural findings consistent with DEB. The results revealed a glycine substitution mutation in all six families, four of which are novel and previously unpublished. In three families with clinically unaffected parents, de novo mutations G2043R and G2040V were found. These results emphasize the predominance of glycine substitution mutations in dominant DEB, and indicate that in some cases the phenotype is due to de novo dominant mutations.

The 97 kDa linear IgA bullous dermatosis antigen is not expressed in a patient with generalized atrophic benign epidermolysis bullosa with a novel homozygous G258X mutation in COL17A1

The nature and expression pattern of the 97 kDa linear IgA bullous dermatosis antigen (LAD-1) and its role in epidermolysis bullosa have not been fully elucidated. In this study, we examined the expression of LAD-1 in the skin specimens of 70 patients with the various subtypes of epidermolysis bullosa, including simplex (n = 23), junctional (n = 15), and dystrophic variants (n = 32). For immunolabeling, we used two recently developed monoclonal antibodies to LAD-1 whose epitopes were ultrastructurally localized in the lamina lucida between NC16A and carboxyterminal domains of BPAG2, as well as autoantibodies against LAD-1 from the sera of two patients with linear IgA dermatosis. Among the 70 patients, only one patient with generalized atrophic benign epidermolysis bullosa failed to demonstrate LAD-1 expression. Although other major basement membrane components, including laminin 5, BPAG1, plectin, alpha6 and beta4 integrins, as well as type IV and type VII collagens were normally expressed, BPAG2/type XVII collagen was absent from the skin of this patient. Mutation analysis on COL17A1 using polymerase chain reaction amplification, heteroduplex scanning, and direct nucleotide sequencing revealed that this patient was homozygous for a novel nonsense mutation G258X in exon 11, and her parents were heterozygous carriers for this mutation. This is the first mutation located in the intracellular domain of BPAG2, and resides 817 bp upstream from the N-terminal amino acid sequence of LAD-1. These findings indicate that the absent expression of LAD-1 is observed in a BPAG2-deficient generalized atrophic benign epidermolysis bullosa patient with mutations in both alleles of COL17A1, and not in other epidermolysis bullosa subtypes. These findings also support the notion that LAD-1 is a degradation product of BPAG2.

Novel mutations in the LAMB3 gene shared by two Japanese unrelated families with Herlitz junctional epidermolysis bullosa, and their application for prenatal testing

The LAMB3 gene encoding the beta3 chain of laminin 5 is a candidate gene for mutations in the autosomal recessive blistering skin disorder, junctional epidermolysis bullosa. In this study, we performed genetic analyses in two unrelated Japanese families with Herlitz junctional epidermolysis bullosa and identified two novel nonsense mutations in the LAMB3 gene. One of them, Q166X (CAG --> TAG), was found in the maternal allele of family 1 and the paternal allele of family 2. Conversely, the other mutation, W610X (TGG --> TGA), was found in the paternal allele of family 1 and the maternal allele of family 2. Thus, probands of both families were compound heterozygotes for these nonsense mutations. Haplotype analyses with intragenic LAMB3 polymorphisms suggested that both mutations had arisen independently in these two families. Both mutations create a premature translation termination codon predicting truncated beta3 chains that lead to absent expression of laminin 5 in the epidermal basement membrane zone. Based on these results, DNA-based prenatal diagnosis was performed by chorionic villus sampling for subsequent pregnancies in both families. Both fetuses were found to be heterozygous carriers of the W610X mutation together with a normal LAMB3 allele, indicating that they were phenotypically unaffected. These findings expand the repertoire of LAMB3 mutations in junctional epidermolysis bullosa, and emphasize the notion that premature termination codons in both alleles of the laminin 5 genes result in Herlitz junctional epidermolysis bullosa.

Predominance of the recurrent mutation R635X in the LAMB3 gene in European patients with Herlitz junctional epidermolysis bullosa has implications for mutation detection strategy

Junctional forms of epidermolysis bullosa (JEB) are characterized by tissue separation at the level of the lamina lucida. We have recently disclosed specific mutations in the LAMA3, LAMB3, and LAMC2 genes encoding the subunit polypeptides of the anchoring filament protein laminin 5 in 66 families with different variants of JEB. Examination of the JEB mutation database revealed recurrence of a particular C-->T substitution at nucleotide position 1903 (exon 14) of LAMB3, resulting in the mutation R635X. The inheritance of this nonsense mutation was noted on different genetic backgrounds, suggesting that R635X is a hotspot mutation. In this study, we have performed mutation evaluation in a European cohort of 14 families with the lethal, Herlitz type of JEB (H-JEB). The families were first screened for the presence of the R635X mutation by restriction enzyme digestion of the PCR product corresponding to exon 14. Four of the probands were found to be homozygous and six were heterozygous for R635X. The remaining alleles were subjected to mutation screening by PCR amplification of individual exons of LAMB3 and LAMC2, followed by heteroduplex analysis and nucleotide sequencing. In three families (six alleles), mutations in LAMC2 were disclosed. In the remaining eight alleles, additional pathogenetic LAMB3 mutations were found. None of the patients had LAMA3 mutation. Thus, LAMB3 mutations accounted for 22 of 28 JEB alleles (79%), and a total of 14 of 22 LAMB3 alleles (64%) harbored the R635X mutation, signifying its prevalence as a predominant genetic lesion underlying H-JEB in this European cohort of patients. This recurrent mutation will facilitate screening of additional JEB patients for the purpose of prenatal testing of fetuses at risk for recurrence.