The molecular basis of lipoid proteinosis: mutations in extracellular matrix protein 1.

Lipoid proteinosis (OMIM 247100), also known as Urbach-Wiethe disease or hyalinosis cutis et mucosae, is a rare autosomal recessive disorder characterized by generalized thickening and scarring of the skin and mucosae. In 2002, the disorder was mapped to a locus on chromosome 1q21 and pathogenic mutations were identified in the ECM1 gene, which encodes for the glycoprotein extracellular matrix protein 1 (ECM1). ECM1 has since been shown to have several important biological functions. It has a role in the structural organization of the dermis (binding to perlecan, matrix metalloproteinase-9 and fibulin) as well as being targeted as an autoantigen in the acquired disease lichen sclerosus. ECM1 also shows over-expression in certain malignancies and is abnormally expressed in chronologically aged and photo-aged skin. Thus far, 26 different inherited mutations in ECM1 have been reported in lipoid proteinosis. In this article, we provide an update on the molecular pathology of lipoid proteinosis, including the addition of 15 new mutations in ECM1 to the mutation database, and review the biological functions of the ECM1 protein in health and disease.

Ectodermal dysplasia-skin fragility syndrome resulting from a new homozygous mutation, 888delC, in the desmosomal protein plakophilin 1.

We report an unusual case of an inherited disorder of the desmosomal protein plakophilin 1, resulting in ectodermal dysplasia-skin fragility syndrome. The affected 6-year-old boy had red skin at birth and subsequently developed skin fragility, progressive plantar keratoderma, nail dystrophy, and alopecia. Skin biopsy revealed widening of intercellular spaces in the epidermis and a reduced number of small, poorly formed desmosomes. Mutation analysis of the plakophilin 1 gene PKP1 revealed a homozygous deletion of C at nucleotide 888 within exon 5. This mutation differs from the PKP1 gene pathology reported in 8 previously published individuals with this rare genodermatosis. However, all cases show similar clinical features, highlighting the importance of functional plakophilin 1 in maintaining desmosomal adhesion in skin, as well as the role of this protein in aspects of ectodermal development.

Three-dimensional imaging reveals major changes in skin microvasculature in lipoid proteinosis and lichen sclerosus.

BACKGROUND: Lipoid proteinosis is a rare autosomal recessive disorder characterized by deposition of hyaline-like material in several organs, including skin. Pathogenic mutations have been found in the extracellular matrix protein 1 gene (ECM1). Recent studies have disclosed that ECM1 is also a target antigen for autoantibodies in patients with the acquired disease, lichen sclerosus. Both conditions have been reported to show abnormalities in dermal blood vessels but these changes have not been fully assessed. OBJECTIVE: The purpose of this study was to investigate the architecture of the cutaneous microvasculature in lipoid proteinosis and lichen sclerosus to better determine the role of ECM1 in the skin pathology observed in these disorders. METHODS: Labeling of skin biopsies (lipoid proteinosis, lichen sclerosus and control skin) with antibodies to type IV collagen and laminin-1 and reconstruction of the dermal blood vessels using laser confocal microscopy and computer imaging. RESULTS: In both lipoid proteinosis and lichen sclerosus there was reduplication of the basement membranes surrounding blood vessel walls. There were enlarged vessels in the mid and deep dermis that were orientated parallel to the dermal-epidermal junction. In addition, the normal capillary loop network in the dermal papillae, as well as the subcutaneous plexus and transverse connecting vessels were lacking in both disorders. CONCLUSION: This study demonstrates that skin microvasculature is grossly altered when ECM1 is targeted by inherited mutations (lipoid proteinosis) or acquired autoantibodies (lichen sclerosus) and that this glycoprotein appears to have an important role in regulating blood vessel physiology and anatomy in the skin.

Development of antigen-specific ELISA for circulating autoantibodies to extracellular matrix protein 1 in lichen sclerosus.

Lichen sclerosus is a common, acquired chronic inflammatory skin disease of unknown etiology, although circulating autoantibodies to the glycoprotein extracellular matrix protein 1 (ECM1) have been detected in most patients' sera. We have examined the nature of ECM1 epitopes in lichen sclerosus sera, developed an ELISA system for serologic diagnosis, and assessed clinicopathological correlation between ELISA titer and disease. Epitope-mapping studies revealed that lichen sclerosus sera most frequently recognized the distal second tandem repeat domain and carboxyl-terminus of ECM1. We analyzed serum autoantibody reactivity against this immunodominant epitope in 413 individuals (95 subjects with lichen sclerosus, 161 normal control subjects, and 157 subjects with other autoimmune basement membrane or sclerosing diseases). The ELISA assay was highly sensitive; 76 of 95 lichen sclerosus patients (80.0%) exhibited IgG reactivity. It was also highly specific (93.7%) in discriminating between lichen sclerosus and other disease/control sera. Higher anti-ECM1 titers also correlated with more longstanding and refractory disease and cases complicated by squamous cell carcinoma. Furthermore, passive transfer of affinity-purified patient IgG reproduced some histologic and immunopathologic features of lichen sclerosus skin. This new ELISA is valuable for the accurate detection and quantification of anti-ECM1 autoantibodies. Moreover, the values may have clinical significance in patients with lichen sclerosus.

Autoantibodies to extracellular matrix protein 1 in lichen sclerosus.

BACKGROUND: Lichen sclerosus is a common acquired inflammatory disorder of skin and mucous membranes. The aetiology is unknown, although HLA-subtype susceptibility and high rates of other autoimmune disorders suggest that autoantibodies to specific mucocutaneous antigens are involved. The clinicopathological similarities between lichen sclerosus and lipoid proteinosis, which results from mutations in extracellular matrix protein 1 (ECM1), suggest this protein as an autoantigen. METHODS: We analysed serum autoantibody profiles in 171 individuals (86 with lichen sclerosus, 85 healthy controls) by immunoblotting of extracts from normal human skin and lipoid proteinosis skin (lacking ECM1). We generated a full-length glutathione-S-transferase fusion protein for ECM1 to confirm specific immunoreactivity. We affinity-purified serum from patients with lichen sclerosus and did indirect immunofluorescence microscopy on normal skin with or without preabsorption with recombinant ECM1. FINDINGS: By immunoblotting, IgG autoantibodies were found in 20 (67% [95% CI 45-84]) of 30 lichen sclerosus serum samples. The highest titre was 1 in 20. The bands were not detected in ECM1-deficient substrate. These samples, and those from 56 other patients with lichen sclerosus, showed immunoreactivity to the recombinant ECM1 protein (64 of 86 positive; 74% [65-84]). Only six (7% [2-13]) of 85 control serum samples were positive. Affinity-purified IgG from serum of patients with lichen sclerosus labelled skin similarly to a polyclonal antibody to ECM1. The positive staining was blocked by preabsorption with excess recombinant ECM1 protein. INTERPRETATION: These findings provide evidence for a specific humoral immune response to ECM1 in lichen sclerosus and offer insight into disease diagnosis, monitoring, and approaches to treatment.

Extracellular matrix protein 1 gene (ECM1) mutations in lipoid proteinosis and genotype-phenotype correlation.

The autosomal recessive disorder lipoid proteinosis results from mutations in extracellular matrix protein 1 (ECM1), a glycoprotein expressed in several tissues (including skin) and composed of two alternatively spliced isoforms, ECM1a and ECM1b, the latter lacking exon 7 of this 10-exon gene (ECM1). To date, mutations that either affect ECM1a alone or perturb both ECM1 transcripts have been demonstrated in six cases. However, lipoid proteinosis is clinically heterogeneous with affected individuals displaying differing degrees of skin scarring and infiltration, variable signs of hoarseness and respiratory distress, and in some cases neurological abnormalities such as temporal lobe epilepsy. In this study, we sequenced ECM1 in 10 further unrelated patients with lipoid proteinosis to extend genotype-phenotype correlation and to add to the mutation database. We identified seven new homozygous nonsense or frameshift mutations: R53X (exon 3); 243delG (exon 4); 507delT (exon 6); 735delTG (exon 7); 785delA (exon 7); 892delC (exon 7) and 1190insC (exon 8), as well as two new compound heterozygous mutations: W160X/F167I (exon 6) and 542insAA/R243X (exons 6/7), none of which were found in controls. The mutation 507delT occurred in two unrelated subjects on different ECM1 haplotypes and may therefore represent a recurrent mutation in lipoid proteinosis. Taken with the previously documented mutations in ECM1, this study supports the view that exons 6 and 7 are the most common sites for ECM1 mutations in lipoid proteinosis. Clinically, it appears that mutations outside exon 7 are usually associated with a slightly more severe mucocutaneous lipoid proteinosis phenotype, but neurological features do not show any specific genotype-phenotype correlation.