PLEC, the gene encoding the cytolinker
protein plectin, has eight tissue-specific
isoforms in humans, arising by alternate splicing of the first exon. To date, all PLEC mutations that cause
epidermolysis bullosa simplex (EBS) were found in exons common to all
isoforms. Due to the ubiquitous presence of
plectin in mammalian tissues, EBS from recessive
plectin mutations is always associated with extracutaneous involvement including
muscular dystrophy, pyloric atresia and
cardiomyopathy. We studied a consanguineous family with sisters having isolated blistering suggesting EBS.
Skin disease started with foot
blisters at walking age and became generalized at puberty while sparing mucous membranes.
DNA sequencing revealed a homozygous
nonsense mutation (c.46C>T; p.Arg16X) in the first exon of the
plectin variant encoding
plectin isoform 1a (P1a). Immunofluorescence
antigen mapping, transmission electron microscopy, western blot analysis and qRT-PCR were performed on patient skin and cultured keratinocytes, control myocardium and striated muscle samples. We found hypoplastic hemidesmosomes and intra-epidermal 'pseudo-junctional' cleavage fitting EBS. Screening for
cardiomyopathy and muscle dystrophy showed no abnormalities. We report the first cases of autosomal-recessive EBS from P1a deficiency affecting skin, while mucous membranes, heart and muscle are spared. The dominant expression of the P1a
isoform in epidermal basal cell layer and cultured keratinocytes suggests that mutations in the first exon of
isoform 1a cause skin-only EBS without extracutaneous involvement. Our study characterizes yet another of the eight
isoforms of
plectin and adds a tissue-specific phenotype to the spectrum of 'plectinopathies' produced by mutations of unique first exons of this gene.