A frequent functional SNP in theMMP1promoter is associated with higher disease severity in recessive dystrophic epidermolysis bullosa

Abstract

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.

Homozygosity for a null allele of COL3A1 results in recessive Ehlers–Danlos syndrome

“…For example, for a same mutation in the COL7A1 gene, different alleles of a frequent functional variant in the gene encoding the matrix-metalloproteinase 1 (also known as collagenase) have been described to produce different forms of recessive dystrophic epidermolysis bullosa. 15 Such modifier genes could also support the marked variability observed in some vascular EDS pedigrees and in the discrepancy between haploinsufficiency consequences in the Schwarze study and in ours. Cis-acting elements could be more easily identified if there is a correlation between phenotype and variations in the expression of the wild-type allele.…”

Immune reactivity to type VII collagen: implications for gene therapy of recessive dystrophic epidermolysis bullosa

“…Type VII collagen expression not only depends on the COL7A1 mutations involved but also on the individual genetic background of RDEB patients. 30 Of the seven RDEB patients studied, four showed no detectable type VII collagen by immunohistochemistry on skin sections (patients 7-10), whereas three patients (11, 12, and 13) showed positive but (markedly) reduced immunostaining at the basement membrane zone. Western blot analysis showed the absence of detectable type VII collagen protein in patients 7 and 8, who are sisters carrying a very early frameshift mutation (Supplementary Figure S2), whereas patient 9, who is a compound heterozygote for nonsense mutations, showed very low levels of full-length collagen VII when 100 mg of protein extracts from fibroblast primocultures (Supplementary Figure S2) were probed using a highly sensitive polyclonal antibody (a kind gift from Dr Mei Chen).…”

Basement membranes in development and disease

“…Patients with RDEB have an increased risk of squamous cell carcinoma, with 70% of RDEB cases leading to squamous cell carcinomas by age 45 (Fine et al, 2009). Polymorphisms in the MMP1 gene are also thought to act as a modifier in regulating disease severity (Titeux et al, 2008). The connection between collagen type VII deficiency, increased collagenase, and squamous cell carcinomas (SCC) is not fully understood, and debate remains open regarding the effect of the loss of BM collagen VII in cutaneous SCC.…”