A recurrent laminin 5 mutation in British patients with lethal (Herlitz) junctional epidermolysis bullosa: evidence for a mutational hotspot rather than propagation of an ancestral allele

Herlitz junctional epidermolysis bullosa: diagnostic features, mutational profile, incidence and population carrier frequency in the Netherlands

BACKGROUND

Junctional epidermolysis bullosa, type Herlitz (JEB-H) is a lethal, autosomal recessive blistering disease caused by null mutations in the genes coding for the lamina lucida/densa adhesion protein laminin-332 (LAMB3, LAMA3 and LAMC2).

OBJECTIVES

To present the diagnostic features and molecular analyses of all 22 patients with JEB-H in the Dutch Epidermolysis Bullosa Registry between 1988 and 2011, and to calculate the disease incidence and carrier frequency in the Netherlands.

METHODS

All patients were analysed with immunofluorescence antigen mapping (IF), electron microscopy (EM) and molecular analysis.

RESULTS

The mean lifespan of our patients with JEB-H was 5·8 months (range 0·5-32·6). IF showed absent (91%) or strongly reduced (9%) staining for laminin-332 with monoclonal antibody GB3. In EM the hemidesmosomes and sub-basal dense plates were hypoplastic or absent. We identified mutations in all 22 patients: in 19 we found LAMB3 mutations, in two LAMA3 mutations, and in one LAMC2 mutations. We found three novel splice site mutations in LAMB3: (i) c.29-2A>G resulting in an out-of-frame skip of exon 3 and a premature termination codon (PTC); (ii) c.1289-2_1296del10 leading to an out-of-frame skip of exon 12 and a PTC; and (iii) c.3228+1G>T leading to an exon 21 skip.

CONCLUSIONS

All diagnostic tools should be evaluated to clarify the diagnosis of JEB-H. We have identified 11 different mutations in 22 patients with JEB-H, three of them novel. In the Netherlands the incidence rate of JEB-H is 4·0 per one million live births. The carrier frequency of a JEB-H mutation in the Dutch population is 1 in 249.

Ultrastructure and molecular pathogenesis of epidermolysis bullosa

Epidermolysis bullosa (EB) is classified into the three major subtypes depending on the level of skin cleavage within the epidermal keratinocyte or basement membrane zone. Tissue separation occurs within the intraepidermal cytoplasm of the basal keratinocyte, through the lamina lucida, or in sublamina densa regions of the basal lamina (basement membrane) in EB simplex, junctional EB, and dystrophic EB, respectively. Transmission electron microscopy (TEM) is an effective method for determining the level of tissue separation and hemidesmosome (HD) and anchoring fibril morphology if performed by experienced operators, and has proven to be a powerful technique for the diagnosis of new EB patients. Recent advances in genetic and immunofluorescence studies have enabled us to diagnose EB more easily and with greater accuracy. This contribution reviews TEM findings in the EB subtypes and discusses the importance of observations in the molecular morphology of HD and basement membrane associated structures.

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.

Bone metabolism in children with epidermolysis bullosa

We evaluated bone mineral density, vitamin D status, and biochemical markers of bone turnover in seven children with epidermolysis bullosa (EB). Four had osteopenia (Z score, -1.5) and four 25(OH) vitamin D <34 nmol/L (14 ng/mL), two of which had hyperparathyroidism. Children with severe EB should have evaluation of bone metabolism.

Herlitz junctional epidermolysis bullosa: novel and recurrent mutations in the LAMB3 gene and the population carrier frequency

Herlitz junctional epidermolysis bullosa is a heritable bullous disease caused by mutations found primarily in the b3 chain of laminin 5 (LAMB3). In this study, we examined the LAMB3 gene for mutations in 22 Herlitz junctional epidermolysis bullosa families, and identified 15 distinct mutations, eight of them previously unreported, bringing the total number of distinct Herlitz junctional epidermolysis bullosa mutations in LAMB3 to 35. Examination of the mutation database revealed several recurrent mutations that have been reported, as well as six previously unreported. All recurrent mutations may be readily detected by polymerase chain reaction of genomic DNA and restriction endonuclease digestion. Mutation screening and prenatal diagnosis of families at risk may be expedited by molecular testing for these recurrent mutations prior to screening the entire gene. Finally, the U.S. population carrier risk for Herlitz junctional epidermolysis bullosa and all variants of junctional epidermolysis bullosa was calculated to be one in 781 and one in 350, respectively, while the overall epidermolysis bullosa carrier frequency was calculated to be one in 113. These data allow accurate testing, counseling, and risk calculation for nuclear families, as well as extended family members at risk for junctional epidermolysis bullosa.